Hello. Tell me at what time did your kids get on their extended arms?…

Hello. Tell me at what time did your kids get on their extended arms? And held the back straight when you were holding them? The baby is almost 4 months old. Turns over only in one direction. No other skills. Doesn't hold his head up for long on his tummy. The baby has 2nd degree ischemia, started worrying that it might be lagging behind.