I have a 13 year old who is just now outgrowing size 16/18. The next size would be small mens and size 29/29 jeans I think. (His last pair of 16/18 sized pants also had 28/28 on them, so I am assuming 29/29 is next, since the 16/18 are starting to get a little snug and high water?)
Guess there isn't much difference to answer your question. Just them growing up and moving to men's sizes.
Other people asked questions on various topics, and are still waiting for answer. Would be great if you can take a sec and answer them