I've been to DLP 4 times now with DS. My advice would be to choose comfortable clothes and shoes and dress in layers. I bought DS trousers which can then be zipped off 1/2 way to become shorts (from Boden) and these worked well. It can be chilly at night whilst waiting for the fireworks etc and early in the morning, so you can change the shorts back to trousers and vice versa.
I usually pack light fleeces to wear in the evenings too. Oh and wear comfy shoes/ trainers- you don't want blisters ruining your holiday.
I would also suggest bringing a pack a mac type thing- even if rain isn;t forecast, you can use it to sit on whilst waiting for the parade/ waiting in line etc.
Sunhats and sun lotion are essential and bring some snacks to eat in queues. If you bring your own water bottle, you can fill it up from the fountains around the park- saves a bit of time and money. Also, the least crowded toilets are in the covered arcade which runs behind the shops to left of main street when facing the castle, when you first get into the park.
Disneyland Paris is a fab place for your hols- you'll love it. Enjoy it and take lots of piccies!