Can't speak for Morales or Akumai, but Tulum is amazing and beautiful. Check out Playa Del Carmen too, north of Tulum.

I haven't been to Akumal yet.

Tulum is stunningly gorgeous, but the town itself is a bit removed from the beaches and the beach hotels are IME a tad pricey. Taxis aren't very expensive, but you almost certainly will need to use them to get around, and that likely means waiting for them once you call for them. BUT it's been a few years since I was there, so maybe things have changed. Definitely a gorgeous beach!

Puerto Morelos felt much more like a "real" place - some resorts on the town's edges, but still a small town where people live and work right on the beach. Great for snorkeling, walking around, some good restaurants (including kid-friendly ones). The beach is pleasant but not drop-dead gorgeous and ruins are a bit further away.

Maybe split your time between the two?

Hope that helps!

I've been to all three, they are all good in their own way.
Akumal has a wonderful beach, great from beach snorkeling, calm safe water. Not much in the way of Mexican culture.
Tulum's beach is very beautiful and uncrowded, but since there is no reef calm the water, it can get rough in the surf. Of course Tulum has ruins and an interesting, funky downtown.
Puerto Morelos has a nice beach (not much shade however), unspoiled, small local Mexican, no ruins close by.
My choice would be Akumal. From here the Tulum ruins are 1/2 hour away.

I've visited those 3 but only stayed in Tulúm. My photos with blog and travelogue links on the main page of each collection are below in case you're interested - all my recommendations are embedded there. Happy trails! http://www.flickr.com/photos/staceyholeman/collections

Thanks for the advice everyone! I really appreciate it.

For enough to satisfy a 9 year old, Akumal for sure. Tulum is amazing for a romantic get away or for doing not much more than relaxing but I'm not sure there's enough to do for a child for more than a day or so. PM is a better choice but I think Akumal would be the best of the three choices.

usr gmaps streetwalk to look the joint over.

Looks like we're spending 4 nights in Tulum and 3 in PM to get a mix. My son really likes nature stuff, so I'm hoping there's enough in Tulum. Thanks.

Akumal is perfect with a 9 year old. Yal Ku lagoon is right there and is a great snorkeling spot plus swimming with turtles right off Akumal beach is a must do.

Tulum is more for romantic get away from it all couples. Often billed as rustic luxury!