Hi Geordieminx,
How many days people like to spend in DLP varies - some like to have a monday - friday trip so they have time to see and do everything without rushing, and maybe go back to their hotel for a while for a swim during the day, or for kids to have a rest or nap away from the noise and crowds. Some people also like to spend a day in Paris, or some time at Val D'Europe shopping mall and sealife centre. Some parents are not very keen on theme parks themselves, and are only going to take their children, so do not want any more than 2 or 3 days there.
For me, it is never long enough!
A 4 yr old child can go on most rides and attractions, as only a few have a minimum height requirement. Adults can go on everything except the two kids play areas in the Disneyland Park.
Rides have to be fitted in around show and parade times, and meeting Characters for photos and autographs etc, which can involve queues ( or sadly some pushing and shoving from some visitors ). Booking a Character Meal is a better way to meet some Characters, or meeting Princes/ princesses, rather than wasting time queueing or being crushed in the parks by some obnoxious badly behaved parents pushing their kids forward with no regard for anyone else.
Two days in the DL Park, and one day in the Studios at a less busy time of the year would allow you to do and see a fair amount, but you may miss some things. You can read about the rides and attractions in both parks online, and make a list of your priorities.
The Disneyland Park is larger than the Studios Park, but has less theatre type shows. It is a good idea to avoid the French and Spanish school holidays if possible, but be aware that you will only see the electrical parade after dark and fireworks at certain times of the year - they are not on every day.
Local French schools have half day or full day holiday on Wednesays, so that day of the week can be busier during term time, and weekends are busy all year round.
Staying in a Disney owned hotel gives Extra Magic Hours from 8am - 10am, when 7 rides are usually open in Fantasyland and Discoveryland. The only one not suitable for young kids in that time is Space Mountain, which is an extreme indoor rollercoaster.
The Studios Park does not have EMH, and closes earlier than the main park. It is open from 10 - 6, or 10-7 at busier times. It is surprising how quickly the time can pass, with stops for drinks, snacks, lunch, loo etc. Moteurs Action Show alone takes around one hour with seating time. Other shows last from 20 mins to around 45 mins.
Ride queue times off peak can vary from 5 mins to 30 mins depending on popularity. At weekends and school holiday time, popular rides can be anything up to 120 mins, although Fastpass tickets can be used to ride in a given timeslot using a separate entrance with shorter queue.
Park operating hours are longer, so you have more time to get things done, and there are usually some extra shows in school holiday time ( like the Winnie the Pooh show in July/ August ) that you don't see at off peak times.
It is worth booking when there is a good offer on - recently Disney had a 50% off flash sale for one week. It is worth checking prices of different hotels on different dates as well, as it goes by arrival date.
My October trip was £ 100 cheaper to go Sunday - Wednesday than on Monday - Weds, flying from Southampton to Orly, even though we have an extra night and park entry.
You can also book with a travel agent, or another company like Eurostar, Expedia, or someone like disneylandparisdirect.com, or shortbreaks.com.
Ledger and Newmarket do Disneyland trips by coach, which are good for people on a tight budget, but does involve a long time travelling.
September is quite a popular time, and can still be hot. French schools go back on 5th Sept, and Spanish schools are similar usually. Mondays and Tuesdays are usually the less crowded days in term time, but they are often the busiest days in the summer holidays.
A very Magical time to go with low crowd levels is in early December for the Christmas Celebrations, although it can be very cold of course, and possibly snow!
People on the Trip Advisor DLP forum that nothinggold mentions will be glad to help.