Hi Liz,
October school holidays are VERY busy in DLP being Halloween celebrations all month, so expect long queue lines and high crowd levels at weekends and after French schools have broken up for the holidays.
This obviously affects how much you can do in a few days. Can you go outside school holidays at all as your kids are so young, or are you tied to school hols?
Santa Fe is the cheapest of the Disney owned hotels where you get Extra Magic Hours usually, from 8am - 10am in the main park. Selected rides in Fantasyland and Discoveryland are usually open.
The Disney car park does cost around ? 15 at peak times, so best to go to your hotel first, check in and get your park tickets which should be included in a hotel/ tickets package. They are valid from arrival day to departure day inclusive so you can then go into the parks.
The cheapest non Disney resort hotel os usually the Kyriad, one of the 5 Associated resort hotels just outside the perimeter road, with free shuttle buses to/ from the parks every 15-20 mins.
There are rides & attractions in both parks for young children - some people say their young kids liked the Studios best, others prefer the main DL Park. There are also shows, parades, with extra shows for Halloween season like Malificents Villains show on Central Plaza stage and Mickeys Halloween Treat in the Street Party show on Royal Castle Stage.
The Disney Dance Express Train also stops at Royal Castle Stage usually with the Characters singing & dancing with kids.
Ideally you need one day in each park with at least one extra day for doing things you missed or favourite rides/ attractions again.
All children are different - some are braver than others - so what rides kids like depends on the individual even if they are tall enough. The Snow White ride in Fantasyland scares many children as it features the dark forest and wicked Queen.
Auberge De Cendrillon restaurant in Fantasyland for Character Dining with Princes/ Princesses is worth the cost if you have Princess mad child/ children but as it is very fine dining kids don't always like the food. You can now meet Princesses in the new Princess Pavilion near Small World ride exit, which opened in the first week of October. There are two Princesses inside at a time, but you only meet one of them as the queue splits to each one. Long queue though.
I would not leave the park to eat unless you really want to, as this wastes time - you have to go through security again to re enter the parks, and there could be queues for this.
If time is limited, buy sandwiches, snacks and drinks ( not glass bottles or alcohol ) from the shop in Chessy railway station that you pass walking to the parks, and take them with you. Many people take extra food from Disney hotels breakfast buffets to make up picnic lunches, but that is not something I agree with. Disney just put the hotel prices up to cover the cost and they may stop including breakfast altogether. ( as in Davy Crockett Ranch from next March ).
You have mentioned Trip Advisor - people on the Disneyland Paris/ Marne La Vallee forums there can help with trip planning for DLP.
www.tripadvisor.co.uk/ShowForum-g2079053-i21935-Disneyland_Paris_Marne_la_Vallee_Seine_et_Marne_Ile_de_France.html
DLRPMagic is also a very useful website for information, menus, prices, ride descriptions, parks maps etc. I think it is better than the Disney website.
www.dlrpmagic.com/guidebook/