Hi OP, I live next to Disneyland 😁 and I'm in Bussy Saint Georges most days too.
Hotel is in a good area. There will probably be a "navette" bus from the hotel to Disney, ask at reception. Otherwise you are only 2 stops away from the park on public transport.
Picnics are banned at the park but it's not unreasonable to bring bottles of water and croissants for quick snacks. There is a Carrefour supermarket at Bussy SG which I recommend for little snacky bits.
In terms of food and restaurants Bussy has some great places to eat actually and because it's not super touristy the prices reflect that. It's got some great authentic Japanese and Vietnamese food, as well as Turkish and Italian. There is also a McDonalds that you can get delivered by Uber Eats at the end of the day. Food prices at the park are extortionate, eating in the Disney Village is cheaper but less practical - McDonalds, Earl of Sandwich, Starbucks and Vapianos are cheaper options.
As previously mentioned there is a huge shopping mall at Val d'Europe, and it contains a massive supermarket called Auchan.
I recommend a buggy board and a pushchair. I also recommend sunshades, hats and sun cream - it's been regularly hitting 30 - 40 degrees in this region for the past 2 months.
Kids medicines are very easily available - but not in supermarkets. There are a lot of pharmacies in Bussy Saint Georges, Calpol is sold over the counter under the name "Doliprane" - there are a few options so make sure you know your kids weight in kgs and in French - my 5 yr old is 24kgs so vingt-quatre kilo 😊
From the airport depending on when you arrive you can take the TGV train (35eur p/adult) not sure how much for kids - which will take you from Paris CDG to the park directly. It's probably more practical to get taxis, just be aware that you will need to ask for child seats prior to arriving. Otherwise the Disneyland coach can pick you up and costs 23euro for an adult and probably about half of that for kids. Definitely have a Google!
Once you're in the park (I used to work at Disney too😅) you'll want to stick to the main park, there's very little going on for small kids at the studios. Fantasyland is good for littles. I think the fireworks are at 11pm at the moment, I will confirm tonight when I hear them 😂