My kids went to the kids club a few weeks ago while we were at WLR. They loved it. They did many activities and ate junk food. The ladies in charge seemed very involved with the kids and we checked on them a few times. So far my kids have had positive experiences at each of the Westin Kid's Clubs that they have been to.
I don't remember exactly what the fee is for any of the Westin's. I seem to remember is being about $35 for a half day and $60 for a full day. I could be off on this so you will want to verify with them directly.
It was free when we stayed there the first week the resort opened in August. We left our kids there for a couple of hours while we shopped across the road at the La Isla Mall. Our youngest was 7. It may be different for younger ones.
Why not call the Lagunamar concierege desk since nobody from TUG has responded in years? The concierge desk will at least give you the fee schedule - or let you know it's free.
I own 3 weeks at Lagunamar. I was last at Lagunamar earlier this year. I'll be there for 2 weeks in January, 2012.
I've seen the Kids Club at Lagunamar. It looks just like the pictures. The kids there seemed to be engaged, happy and well-tended. But, I don't usually travel with kids so I don't really know what goes on at the Kids Club.
Lagunamar's a pretty cool resort with the Kids Club and a waterslide in the pool. It also has a McDonald's, a Haagen-Daaz, a Planet Hollywood, a Chile's and an Aquarium (and 2 Starbucks and various other restaurants and shops for adults) in the La Isla Shopping Center right across the street from Lagunamar.
My only caution would be: do not let your kids swim unattended in the surf. It's pretty strong with a rip tide (but that's the way the surf is all over Cancun). ... eom