We are frequent DLP visitors (we have annual passes); I've only been once to WDW and it was a long time ago, so cannot really compare the two.
But I love DLP

I find it the most beautiful park there is. The Studios... well, I'll get back to them. But the Disneyland Park is simply stunning. I do believe we have the most beautiful castle there is, Main Street is full of great little details, Fantasyland is a thing of beauty, Adventureland is a lush, green bit of heaven, and Frontierland well it's the best land of them all...
I've just done a
Disney Cruise and have a much better understanding of why Europeans (and CM in Paris) have a bad reputation... I've always found that if you're nice and friendly to them they're nice and friendly back to you, and personally I usually have a great experience with the CM in Paris - just don't expect an American level of service. Fellow guests, on the other hand, can be pretty awful

. There will always be people around who seem to think that they're entitled to do whatever they want whenever they want, without any consideration for the other guests, let alone any respect for the work done by the cast members. Now in the summer you're sure to find guests lying down in the grass (behind the fences), standing on flower beds... Not to mention smoking everywhere (worst I've personally seen was someone smoking INSIDE Its a small world....). They're also very keen on trying to jump a queue, or pushing their way to the front after showing up 2 minutes before the parade starts. Personally that's one of the reasons I try to avoid the busy seasons, it's not only to avoid long queues but also to avoid having to see too many people destroying my beautiful park... Don't get me wrong, most guests are perfectly polite and considerate!!
We took our daughter for the first time when she was 18 months old, and since her second birthday she's been going quite regularly. I find that it's best to take it easy with her, and not to try to fit too much in (particularly if there are long-ish queues). She loves meeting the characters, we usually go to Meet Mickey Mouse in Fantasyland; we usually wait between 30 and 40 minutes, but there's a big screen showing Mickey cartoons while you wait, so at least our daughter never gets bored. If the budget allows it, go for a character meal. Inventions in the Disneyland Hotel is great (characters are there for dinner in the evenings, and for Sunday Brunch) - plus as in all buffets children under 3 don't pay! Otherwise there's Cafe Mickey in the Disney Village, personally I find it a bit noisy, but it can still be a very fun experience.
In terms of rides, she loves all in Fantasyland - one of her favourites is Alice's Maze, we let her guide us around it and she loves being in charge. In Discoveryland Buzz Lightyear's Laser Blast has always been her favorite. She doesn't like Pirates of the Caribbean (and is probably scarred for life after doing Phantom Manor once

), but I've seen plenty of kids loving POTC

. In Adventureland we like going around the caves in Adventure Isle looking for the treasure. And in Frontierland she really likes taking the riverboat and try to find the local wildlife (there are a few birds around...). For the parade, I usually try to find a spot by the start (in the back of Fantasyland, by the Bella Notte restaurant), I go there about 30 minutes before the parade is due and usually there are still plenty of good spots around. My husband usually takes our daughter to do one more ride before joining me - so that she doesn't need to wait long.
The Studios... well, they're a work in progress. They used to be pretty awful, now they have some good areas (and some not so good). The new Ratatouille area is beautiful (and the Bistrot there one of our favourite restaurants in the resort!), and the new ride is brilliant (although personally I feel a bit sick, I don't handle simulators very well

) Then you have Toy Story Playland, it's quite cute. Elsewhere you'll find Crush (very long queues), Cars (our daughter loves it), and the Flying Carpets (another favorite for our girl). For the grown ups, Tower of Terror and Aerosmith are brilliant. Don't bother with Armaggedon...
The Studios have a few shows; Animagique will probably be a must for your little one. The adults will probably enjoy more Cinemagique, it's really something not to miss. Then you have Disney Jr Live on Stage, which I really could live without (particularly since it features shows no one really knows anymore!), but my daughter always insists on going because before the show starts (about 15 minutes before) princess Sofia and Jake from the Neverland Pirates come out and dance with the children.
We usually spend about half a day in the Studios, and the rest of the time in the Disneyland Park.
Our daughter was always been a good sleeper so we can usually leave her in her pushchair and stay around the parks - or we go to the Disney Village for a coffee from Starbucks, and stay around the Fantasia Gardens where it's nice and quiet for her to sleep. Even now that she's 4 she still needs at least a little nap, a day in the parks can be exhausting!
I don't know when you're thinking of going, but personally I would avoid the summer. September can be good (if weather is good weekends will be busier). October is Halloween, a great season (and weather is quite reasonable). And from November it's Christmas, plenty of magic to go around (though it's incredibly busy, particularly on Saturdays). Between January and March (excluding school holidays) it's usually nice and quiet (but may be cold and wet...)
Apologies for the extremely long answer

... But there are some subjects for which once I start, I find it difficult to stop
Have a great trip!!