We had the breakfast at Cafe Mickey in June and it was lovely, the characters work their way round the rooms (there is one big main room and a sort-of conservatory at the side from what I could see) and spend time at each table posing for photos, signing autograph books and they are really good at making sure that every child at every table gets seen, and no-one is forgotten
The food was quite similar to the hotel breakfasts - pain au chocolat, croissants, toast, bread, jams and marmalades, fruit salad, ham and cheese, and then there was sausages, scrambled eggs, and bacon I think! I'm sure you will find something your sons will love, and even if they just have something plain like toast it will still be worth the money because it is lovely to be that close to the characters and to get all excited as you know they are getting nearer!
As for the weather, yes in my experience it is very similar to the UK - although I have heard people say that they weren't quite prepared for the winter months and wish they had taken more layers so that may be worth keeping in mind
I think things like taking more socks and shoes than you need just in case of bad weather, that sort of thing, is a good plan.
DLRP Magic is an amazing site, definitely worth having a look at! If you use that site or the Disneyland Paris official website, you can find out more about the rides. I would recommend It's a Small World, Pirates of the Caribbean (if they don't scare too easily!), Le Pays des Contes de Fees (Storybook ride), Casey Jnr, Mad Hatter's teacups, the Carrousel...erm...trying to think now...Dumbo! Fantasyland is a perfect land for smaller visitors, lots of child friendly rides. If you have a look at some DLP sites, you can see the different rides in each land and make a list of what sounds suitable, so you know where to head to when you arrive.
Hope you have a great time!