Young kitten mewing when pooing - concerned?

[Moln]

I'm looking after a nine week kitten, he's been with us a week now, he's litter trained but recently he's started mewing when he's doing a poo. It's drawn my attention because he's a quite thing, only time he mews is when my 7 year old picks he up when he doesn't want picking up.

Should I be worried? I'm a total novice to kittens!!!

When he is doing a poo or before? Mine warns everybody she's entering the litter, however she is very vocal most of the time (chatty kitten!)