been here a few times, the first time i took the children the youngest was just 1 and the eldest had just had her 3rd birthday. the last time we went was a couple of years ago when the junior blues were 6 and 8.
in terms of how long you need to go for to see everything, i'd say it depends on how old your children are and what time of year you go. if you're going in august the place will be mobbed and it will take you longer to get around / queue for attractions. the firts time we went was the last week in september and the parks were much quieter.
where you stay can also be a factor. if you stay in one of the disney hotels, park tickets are included in the price and you get the benefit of "extra magic hours" where you get early or late access to the parks and certain rides.
also, don't waste your time queuing up to meet characters, book a character meal where they come to you.
i normally book flights with air france, hotels direct with disney then a taxi transfer to and from the hotels / parks or expedia have some decent package prices.
finally, not that i would ever advocate that you cheat on bm with another forum, have a look at <a class="postlink" href="http://www.disboards.com" onclick="window.open(this.href);return false;">www.disboards.com</a> and look at the board which is about disneyland paris. as with any forum, there are a few nutters about but its good for general planning and information.