We did this with 5 and 6yo DDs. It was truly magical. You will love it.
We did three days in main park and one at the universal.
I would only do the main park if I went again. Universal is small and more for older kids.
To enjoy your days you need to plan, plan and then plan a bit more. We went with the flow on the first day, kept missing stuff and ended up tired and fed up.
The second day we were very organised and it was so much more fun.
Get a guide book and read before you go. Each day a daily flyer tells when and where parades/ character meet and greets are. We spent lots of time getting autographs!!!! Study the daily flyer and make a plan of about five activities e.g. Meet mickey, then go on a ride, then watch parade etc. plan your route around park.
I know this does not sound much fun, but believe me it makes the day much better.
You also need lots of drinks and snacks. You can fill your rucksack with croissants, drinks etc. but you are not allowed a pinic basket or hamper.
If you take screw top bottles you can refill for free at the fountains.
Make sure you get a good place for the parade on Main Street. It is worth sitting down an hour before it starts and using this time to have a picnic whilst you take turns doing toilet trips. It is worth sitting just at point of steps of the castle as the parade stops here and the characters come to the edge and choose children to dance with - it is just lovely.
We only stayed for the fireworks one night and they were fab.
We paid 15 euros a day to park in the eurodisney car park so be aware of this and there was also a toll road on the way. It is too far to go back to car so take all you need with you.
We got away without buggy, but 4yo needed lots of drinks/snacks to keep going. You really can't take too many!!!
Have a brilliant time.xxx