Pekins dont reach there potential size until about a year old and for showing are at there max pontential till 2 years old, they wont grow much more in hieght they will get heavier though. you can usually tell what you have at 4 months old, but you have to think too birds dont grow well in hot weather so this really slows them down so they should continue to grow very slow. Pekin drakes should weigh 8 pounds as cockerels and 9 as adult 1+years giving a 20% varience either way 7.2- 10.8 pound range. but yours are really young they should still grow some!