You might want to try posting this on the Home Decorating forum. Also, check out the Gallery on the that forum.

both my boys have 2 different blue rooms. my oldest picked it himself and it is a darker blue. but my youngest was only 20 months old at the time and i wanted something lighter, but at the same time grow with him so we don't have to repaint after 3 years. it is Sporty blue (6522) sherwin williams. We love it! it goes with everything. he is currently into the same thing as his older brother. and it matches also. I got my husbands old spiderman comics and put them into black frames and it is really cute.

I love a BM blue paint chip called Clear Skies. I'd love to try it in a bathroom or nursery someday. According to colorcharts.org, a similar SW blue would be Bubble 6770. My sister-in-law picked more of a medium blue for my nephew's room, and it really seems too dark for a child's room. If you want cheeful, I'd keep it light. Checking out the blues on the favorite paint colors blog might be helpful, too. SW Waterscape and SW Tidewater look pretty and cheerful.

Here is a link that might be useful: Favorite Blues

(self-editing...''cheeful'' above should've been ''cheerful'')

I also like SW Meander Blue, which was easier to find online pics of than Bubble was.

Try BM Light Blue and Honolulu Blue. The Honolulu Blue was a little too bright for my son's room at 100% but the 75% formulation was just the right kind of cheerful. These are BM colors but you could get SW to color match.