[jacobolus]

For any parents who want to help their small kids’ balance, let me recommend holding them by the hips for a few minutes at a time starting from about 5 months, instead of holding them by the armpits.

If you hold them from the top they will be passively stable, but if you hold them from the bottom they will need to actively stabilize themselves using their back/abdominal muscles. If you start with just 1 joint they need to stabilize, they figure it out reasonably quickly. (Babies start out surprisingly strong; what they completely lack is coordination.)

After about a month of that, you can carry them around on your shoulders and they will be able to hold up their torso and stay upright. This is great core strength/balance training, while also being a lot more convenient than any other way of transporting a baby, for a moderately healthy parent.