Should I be concerned with my childs growth?

[Guest guest]

I have one child that has a Russel silver syndrome which has caused a

growth delay. He will be 13 in January.He is 4ft 3 inches.The drs only

expect him to be a little over 5 ft when he is done growing.Now My 1

year old(just turned 1 in november) is extremly small also but has no

russel silver syndrome traits.He is 16 lbs and stands 27 inches tall

right now.When should I ask the Dr to send him to a specialist?My 3

year old is big for his age and the new baby I am going to have is

going to big for the gesational age.I gues I'll have all matching pairs

lol.