good on u for checkin ahead, stuff like this can catch ppl off guard. for france, there's no official rule sayin u need extra docs as a solo parent if ur both UK citizens, but it's def smart to carry a signed letter from mum just sayin she's aware of the trip n gives permission. maybe include her contact info too. border staff prob won’t ask, but if they do, better safe than sorry. enjoy the trip with ur lil guy, france is a great shout 🇫🇷