We went in October with our nearly 4 year old and had a fantastic time. We were lucky with the weather and it was relatively warm and dry for our whole stay which was great. Layers are the best bet.
I think our DS's favourite rides were Buzz Lightyear and Autopia in Discovery Land. Peter Pan and It's a Small World in Fantasy Land. Plus, right at the back of the park are a little circus train ride and a fairytale boat ride which he enjoyed and are specifially aimed at the younger guests. In the studios he enjoyed the Flying carpets, Cars quatre roues rallye and Slinky Dog.
Food is really expensive and not great but we stayed half board which meant we had a big breakfast in the morning at the hotel (stayed at the sequoia) which kept us going, with a snack in the afternoon (I took some snacks like cereal bars with us and we grabbed apples from breakfast). Then we had an early dinner back at the hotel where we had unlimited access to a fairly extensive buffet.
We booked character dinning in The Mickey Cafe one night (definitely book in advance for a reasonable time slot). Our DS enjoyed seeing the characters but he's very shy so didn't want to be hugged or have his photo taken with them. Food here was pretty bad too but I guess it wasn't really about the food.
The biggest downside to the visit was the smoking. Sometimes it felt like we were the only people in the whole park not smoking.
I can recommend the free Disneyland Paris app. It gives you the current wait for each ride and allows you to quickly locate your nearest toilets or restaurants etc which is really handy. We used this in addition to the paper maps and guides they provide and found it really helpful.
We didn't have a plan before we went and decided to just see how it panned out. We were there from Wednesday to Sunday though so had plenty of time. I think if we had tried to do it all in a couple of days we'd have needed to prioritise certain things. Also check which rides or attractions will be closed for refurbishment when you are visiting.
We had a fantastic time and I hope you do too!