IMHO you can't go wrong with the BM Pottery Barn colors. You can look online and see what has been on the list this years and in years past.
BM Hawthorne Yellow was on the list last year and seems to be a sunny yellow.

I used Behr Havana Cream in my son's room. I would describe it as "lemon-y" rather than soft and buttery. (Maybe I'm hungry?) The room is south/west facing and gets tons of sun. I'll post s few different pics so you can get an idea... There's also a couple more recent pics in the post called "Is this mirror too high?" but the lighting is not the best for viewing the paint color.

(Pics are taken w/ natural light, no flash.)

Hawthorne Yellow has been on the BM Pottery Barn list for many many years now...I have always wanted to use that color! I used Windham Cream which is a softer, creamier yellow on the same card as Hawthorne Yellow. (Both BM Historic Colors). I have also seen Hawthorne Yellow in a friend's living room and it is what I would describe as sunshiney but not lemony, not taxi cab, not highlighter...just a pleasing pleasant sunshine yellow. I also read on a blog a few years ago, that Hawthorne Yellow is that "perfect yellow" that most people look for in the home. Good luck! :) Let us know what you choose!

Another vote for Hawthorne Yellow. We used it in our windowless basement bathroom with dark cabinets and trim and white counters. It looks fabulous! A bit sunnier than we had anticipated for a bathroom, but it would be perfect in a playroom. Sorry I don't have a pic.

Citron Paint out of Tuscon AZ = full spectrum paint - some of the creamiest, best paint around - LOVE IT! Expensive but the colors are fantastic!
The colors:
http://www.citronpaint.com/daub%20sheet.pdf
The main page: http://www.citronpaint.com/
A previous home - Lantana is the color of this yellow.

Another vote for BM's Hawthorne Yellow. I used it in my kids' room and it feels like pure sunshine. It's not lemony, green, or nuclear. Just warm, sunny, and happy. I am thrilled with it!

I agree with nutmegxo. I wanted my DD's room to be a bright yellow and ended up with eye an piercing yellow that tires your eye. I tried another light yellow in a tenant's apt but it was horrible - actually cold and took 3 coats to cover. I wanted a warm sunny kitchen (south and east windows) and someone suggested using BM Hawthorne Yellow. I thought it wasn't yellow enough. I was wrong. It's wonderful and exactly the right warmth and yellow. I also used BM Windham Cream in the hallways. It's much lighter. I think Hawthorne yellow would be a great choice for a children's playroom.

Thanks for all your helpful replies and for the photos!

I went into my BM store today with the express intention of buying a sample can of Hawthorne Yellow based on the recommendations here.

I walked out rather dubiously with America's Heartland! And I'm still dubious after painting a swatch on the walls. It's so light! The guys at the store said I'd be happy with that considering how I felt about York Harbor Yellow & Suntan Yellow (which look so orange now in comparison to America's Heartland).

I will say that it's a very "clean" yellow but I'm wondering how such a light yellow will hold up to two 4-yr olds.

I may be going back for Hawthorne yellow!

BTW - when did the price increase on samples? I swear the last time I bought some a few months ago it was $6.99 and I KNOW last week I paid $6.99 (but of course, I can't find the invoice). Today, I paid $8.39 per can!

I think Hawthorne Yellow is available in those tiny vials of ready-made samples. You don't have to have them mix up a sample for you. I forget what the price is on those little vials.

Have you gone to a larger BM store, they have large sample sheets of some of the popular colors.

Hawthorne Yellow is a bright classic yellow.

Well, I've decided to go in another direction. Call me chicken for not wanting to try to find the right yellow. :)

Here is my new "old" inspiration - old because I pinned it to pinterest 23 weeks ago!

{{!gwi}}

We actually already have most of these shades in play around the house so it seems like the perfect, fun way to bring them all together in one room.

Now I just need to find the perfect green, lol. That is the color my 4yo DS wants. I'm struggling between BM Apple Green (his FAVEOREET!) and BM Hibiscus.

BTW - thank you for all the help again. Verbalizing this with others who are always thinking of color helps. I showed DH this photo:

and he said that from his perspective it looks exactly like the current color in the playroom:

{{!gwi}}

See what I'm up against? LOL

madtown - your son's room is lovely. That is actually very similar to the color that is in my son's room right now. I do like it but it's a bit hard to keep finger-print free and clean. :)

EG3d - Citron paints are gorgeous! I've admired them from afar but they're just not in my budget.

Now...to figure out this stripe thing. Yikes!