I can only echo the replies from other posters -- there is so much at DLP for the young ones to enjoy. We visited Paris in mid-September and enjoyed a day at DLP as a vacation from our vacation. Aside from doing the baby-swap on Indiana Jones and Space Mountain, DD (also 4.5) enjoyed everything. FYI -- we went on a Wednesday, every ride was a walk-on save for the 5 minute wait at Casey Junior and about 6 minutes at Dumbo. There was nobody in line at Pirates!!!
Phantom Mansion -- she loved it. We did this one twice.
Big Thunder Mtn. -- nice introduction to roller coasters for the little one. Used a Fast-Pass here after enjoying Phantom Mansion.
Tarzan -- great show and participation for the youngsters. Try to sit in the front rows and the child might be brought forward for the Breaking up the Camp music.
Pirates of the Caribbean -- nothing to be scared of here. Good pirate fun and a great sing-along-song. The pricing at the adjoining restaurant isn't out of line with the food prices one might pay in the city of Paris.
Casey Jr. -- another great roller coaster introduction with great theming.
Fairy Tale Boats -- try and remember all the fairy tales you thought you forgot. Spot Belle reading by the fountain -- take this before you take Casey Jr. and you'll soon realize why Cinderella's castle is up so high.
Small World -- this one puts to shame IASW at WDW. I hope the WDW refurb uses this one as a minimum standard to attain.
Peter Pan -- what can one say about soaring over London in a Pirate's ship? So much fun.
Snow White -- DD thought it somewhat scarey, but the movie is too.
Pinnochio -- same thoughts as Snow White, but every Disney classic has its dark side.
Space Mountain -- as I mentioned before, we baby-swapped on this one. Do the swap -- once again, this far outstrips Space Mtn at WDW. The Jules Verne theming is wonderful.
Nautilus -- it's a walk through, disappointing if the child (or the parents, for that matter) are expecting a ride.
Space Tours -- great for children, although peculiar to hear C3P0 talking French with a British accent. The ride commentary itself is in English and is exactly the same as ST at WDW, from what I could tell.
Lion King -- get your tickets early, we didn't know there were tickets needed for this show and had to stand and watch from the eating section. Still, the characters come right up into the audience (including as far as the restaurant section) and interact with the audience. DD enjoyed this.
Dumbo -- it's Dumbo, enuf said.
Carousel -- see Dumbo.
Alice in Wonderland Maze -- DD enjoyed this as she was in an "Alice in Wonderland" figure skating show in the early spring.
If the crowds are low DLP Magic Kingdom is the perfect park for a day at leisure.