Does early sitting harm my baby's back?

Your worry about early sitting is very understandable. Propping your baby with pillows to sit is different from them developing the skill to sit on their own. Babies typically start sitting unsupported between 4-7 months; this happens when their back and belly muscles are strong enough.

Spending a short time in a propped-up position (for example, 5-10 minutes, a few times a day) doesn't cause permanent spine damage. However, if your baby can't hold themselves upright yet and is completely relying on the pillows, this position can strain the spine's natural curve and isn't developmentally appropriate. Especially if your baby's head is tilting forward or their back is extremely arched backward, this is a sign of early and prolonged propping.

Current pediatric opinion is that letting babies develop at their own pace is healthiest. If your baby looks comfortable and happy in pillows for short times, there's no problem. But if they seem to be straining, fussing, or slumping, stop that position and put them on their belly on the floor to play — this naturally strengthens the muscles needed for sitting. If your baby still can't sit unsupported by 7 months or you notice significant imbalance while sitting, I recommend consulting your pediatrician.