special needs?

i watch my nephew during the week, and he's about 16 months old, and the more i watch him the more i notice he's not extremely developed compared to other children i see... he still doesn't walk completely right, he doesn't say any words besides mama, he also doesn't babble a whole lot, you can call his name 20 times and he won't even turn to look at you, if you point at stuff he won't look in th direction, and just other things like that.. do you guys believe hes not completely there? i don't mean this in a mean way either, i'm generally concerned and his parents don't think any things wrong with how he is... he's also fallen off the bed a lot and even busted his lip once or twice but they never took him in to the doctor so i feel like that is part of the reason why too..