Hi, I've not been on this yet, but my 11 year old dd has, and said it's definately not suitable for younger children, and has warned me against it for her younger brother, age 4.
I checked disneylandparis website which says not suitable for children under 8 years. The site is good for checking, but can be quite time consuming.
I'd say that most of the rides in Fantasy Land are ok for 3 year olds:
Peter Pan's Flight
Dumbo's
Teacups
Carousel
Small World (the tune will stay with you all day)
Story book land (i think thats what its called - boat ride)
Casey Junior train
I'd avoid the Snow White - mainly has the witch and is dark, hence the reason there is never a queue
Pinnochio is much the same as above.
My elder ds loved Big Thunder Mountain and Pirates of the Caribbean, but not sure my youngest will, he doesn't like fast things or the dark, so i suppose it depends on your own kid.
Take some time to look on the disney website for ideas.
Hope this is of some help, have fun!