I thought that about the kid, seems a bit on the wee side for 6, but think about it, post apocalypse babies won't have access to the same nutrition and vaccinations etc so would most likely be underdeveloped compared to modern day kids. Either a bit of an oversight by the casting crew or incredible attention to detail?!
Judith looked like she grew up healthy enough, as did the kid Grace who Aaron is looking after - the baby they took from one of the saviour outposts.