Today's answer is from a guest expert--my brother, who is a carpenter in a midwestern US city. You'll see where my "let's figure it out by talking through it" style must be a family trait.
"I am very crafty and have all the tools to make my 15 month old a set of lovely wooden toys, but am a bit wary of which woods to use. I'd like them to be a set of stacking blocks that is pretty primitive, with bark still on parts of the pieces, but don't know which woods would not be advisable for a toddler that still likes to put toys in his mouth. My preference would be to make them from a native (to our area in Texas) pecan or cedar, as I have much of that lying around waiting for my projects. I tried googling, but didn't get any helpful info. Do you have any ideas of where to look? And what kind of oil/finishing treatment to use if any?"
My brother (should I give him a pseudonym?) answers:
"Wren (and Moxie),
I did not have much luck with internet searches for kid-safe woods either, other than people who were selling wooden toys of mostly unspecified species of woods, so I am going to have to turn to my own experience, anecdotal evidence, and picturing my intended block user.
As to the specific woods the question mentions, I don't know enough about them to be definite that they are baby safe. The cedar I have worked with here in the Midwest tends to be soft, and splintery, and something in the cedar oils that make it rot- and bug-resistant tends to make the slivers it produces much more irritating (they burn!) than other woods, so I suspect there may be something sort of toxic in cedar. I would be willing to assume the same about redwood and any other naturally insect- and rot-resistant woods. Also, in ALL cases steer clear of pressure treated woods, a la the wood used for decks. This exterior grade construction lumber is regular SPF (lumber industry jargon for an unspecified coniferous softwood that could be either Spruce, Pine, or Fir) that has been treated with chemicals that kill fungus, microorganisms that lead to rot, and insects. But anything that is killing bugs and germs is probably not good for kids, and in fact, up until a few years ago the main treatment was a chemical stew called CCA, chromated copper arsenate, three things your kids should not be touching, gnawing on, or inhaling. The copper gives treated deck wood a greenish tint, so you can fairly easily see it when you run up against it. Also not good for kids are railroad ties, as they have been treated with all sorts of rot-resistant chemicals, like creosote, and while they are all over in landscaping, they are full of nasty things. The sawdust these treated woods produce are a toxin that makes your nasal passages sore and it is nasty stuff.
I have no firsthand experience with pecan, but thinking about it, here are the qualities I would
generally look for in wood for blocks: fine grain, and relatively unlikely to produce splinters. Mahogany, walnut or oak would be examples of grainy wood prone to making splinters. Maple, birch, cherry (although cherry is somewhat toxic, if I remember correctly from my campfire cooking days), and even slow-growth pine, fir, and spruce tend to have finer grains that in my experience are less splintery. If you do choose to work with woods similar to the first group, make sure your tools are sharp to minimize chatter, tear-out, and splintering, and pay special attention to sanding them extremely smooth before letting your child handle the blocks.
I would think twice about keeping the bark on the blocks, for a couple reasons. First, if your young builder is like I was, eventually there will be tall towers to build, and with the irregularities of shape that the bark would leave, that Empire State Building might come out more like the Leaning Tower of Pisa, or simply topple over before it was appointed toppling the tower time. But more importantly from a safety standpoint, as wood naturally ages and the moisture levels change, the bark layers tend to separate from the rest of the wood. Knocking blocks around, tumbling down structures, and chewing on edges would tend to accelerate the bark falling off, and would leave small pieces of bark loose to be put in the mouth or nose, or ear, or anywhere else kids stick small objects.
All that said, the blocks I played with and drooled all over for years and years of my childhood were a lovely tight grained pine or fir, and a few maple ones thrown in for good measure. The only finish was hand sanding to a very smooth finish (probably with at least 240 grit sandpaper. FYI, in sandpaper the higher the number, the finer the grit and the smoother the resulting finish, so for kids toys I would sand as high as 320 grit if possible) with the edges relieved, and oils from my fingers and face and whatnot as the only preservative.
If you do want to put a finish on the blocks, linseed oil, which is the original oil base in oil-based paint, is an excellent natural oil for wood. It is simply non-foodgrade flaxseed oil. (linen=flax fibers, lin-seed = flax-seed) In hardware or art supply stores you often find "boiled linseed oil," but as the wikipedia article mentions, if you are not careful in checking the label, you may be getting some metallic and petroleum content in your flaxseed. Plain foodgrade flaxseed oil would probably be very good for treating kids' blocks. Olive oil is good and safe, but I don't think it has the longevity of linseed oil so to keep the same sheen you would have more frequent reapplications. (I think there is a chemistry reason having to do with the eventual breakdown of fat molecules in oils, and the tendency of foodgrade oils to eventually become rancid. I looked for some Alton Brown references to oil/fat chemistry, because I remember him doing a good explanation of cooking oils, but I couldn't find it.) Another foodsafe option is mineral oil (a.k.a. baby oil), which has been used as a preservative on butcher blocks and cutting boards, and as a sealer of stone food surfaces, for generations. Kids playing with blocks would probably give them a natural low luster even when the oil dries out, but reapplying oil as the blocks dry out will keep a low luster finish when no kids are polishing them up with their little hands.
Again thinking back to my trusty childhood blocks, I suspect the set was made from 2x building material cut and sanded by someone into some fantastic, cheap modular blocks. I would still use SPF construction lumber softwoods, but in the intervening 30+ years, construction grade lumber, as in all wood products, has had a marked decline in quality. We have used up all the old growth trees. SPF construction lumber is a farm system now, growing hybrid trees that grow fast with many knots and wide splintery grain. Slow growth makes for tight, stable, generally less splintery grain. Every year it is harder, and consequently more expensive to find good quality wood. Luckily, for blocks we are not talking about large pieces of wood, so we can cut around knots and bad grain. Knots can be aesthetically lovely in wood, but in pine, fir, and spruce they tend to be where the sap and tar accumulate (they are sticky), are harder than the wood around them (that makes sanding them difficult), as the wood ages they change moisture content differently than the wood around them (so would be prone to falling out, and would be hazardous the same way bark could be in a set of blocks) and knots resist any oil treatments for finishing.
So choose your wood carefully, especially if you are buying it at a big box store like Lowe's or Home Depot, where the price is low because the grade of wood they sell is the bare minimum required for construction. If you are not interested in cutting around imperfections, you might go to your local (I mean local, not part of a large national chain) lumberyard and asking them about obtaining a better grade of softwood, or a decent grade of hardwood (big box stores have very poor hardwoods generally) if you are interested in working with something more elaborate than pine. The price may be higher than a construction grade SPF 2x4 at Lowe's, but because blocks are small sections of wood, you can probably negotiate for scraps and cutoffs local lumberyards often have left over from large orders others have already paid for. They may even give it away to you if the pieces are small and they want to get it out of their warehouse or yard. Along that line, you might even try local manufacturers who use wood. Where I work right now we use thousands of board-feet of low grade wood every day, and in the milling process we have thousands of board feet of scrap we can't use in a week. Consequently, we have scavengers who stop in weekly to fill up trucks for local reuse as firewood, my coworkers take home scraps for various projects or bonfires, and the rest is eventually shipped off to be recycled as any number of forest industry products. Because kids' blocks are small, it would be very easy to find enough usable pieces from the scrap of most wood-using businesses to make a great set of blocks. All you need to do is ask nicely and there is a good chance your material could be free.
I'm not sure if that answered your question adequately, but I hope somewhere in the large quantity of response you find some quality info you can use."
There you have it--more than you thought there was to know about making kids' toys with wood.
Book review up this evening.