if your little grandson is on the chubby side the penis can be hidden by a surrounding fat pad quite common in children. if you push on the fatty area around his penis and the penis seems to emerge like turtle coming out of a shell then it is probably just fine. there is a medical condition called a "hidden penis" and another relatively-rare condition called a "micropenis" that you read about on an internet search but it may be too early to know if he has any of these unlikely conditions. bringing it up to the pediatrician at his upcoming one-year examination would be appropriate.
my grandson age 10 months penis hardly visible testicle size normal. is this cause of concern and further investigation