This is something no one tells you: Being a parent is like doing CrossFit with a really strong, risk-taking, ill-tempered-but-adorable monkey trainer. You will sustain physical injuries.
Let's not even talk about pregnancy and delivery. Let's talk about tennis elbow and tendinitis from carrying the baby. Back problems from hunching over while feeding the baby. Concussions from toddlers and preschoolers. Chronic sleep problems.
This is no joke. It's painful, and it's hurtful, too. Physical pain hurts your feelings. And most of this pain happens long before your child is old enough to understand and be careful of you physically.
There will be a day, however, when your child begins to understand that they can take as much care with you as you take with them. When your child starts protecting you and your body as much as you protect your child. It takes years, and a lot of stress on your body, to get to that part of the conversation. But you'll get there.
In the meantime, lift with your legs.