Me and my buddies love to ride play bikes. They are a blast because they are so slow and super quiet. We can ride them all day without much work. However, the one problem we always have are with the wheels. Play bikes come with wheels made for beginners and they just don't hold up to the hours and pounding me and my buddies put on them. It doesn't help that the track I ride on everyday has tons of square edged rocks, let's just say I've broken a few wheels and flatted my fair share of tires. After me and my riding buddies had exploded, what my dad said was our last wheel, he showed us some tips that would keep our mini bike wheels alive.
These tricks are especially important on the play bikes like the CRF50, KLX110, DRZ70, etc. but can be used on all bikes. The play bikes come with steel rims that are bendable and have weak spokes. I don't think they are made to get the big air like me and my buddies like to do, but it's just so much fun.
The first thing is to run at least 20 lbs. of air. A lot of times I'll run up to 30 lbs., especially on the 10" wheels. If you run the normal 12 - 15 lbs. like you would on a big bike, you can count on exploding your play bike wheels fast. The bike takes a little getting used to at this air pressure, but it's so much better than not riding because of a broken wheel or flat tire.
The second trick is to keep the spokes tight. Usually I start at the valve stem and work my way around by tightening each spoke nipple 1/4 of a turn, all on the right side. Then 1/4 turn on the left side. Don't over tighten the spokes! They need some room to flex. Snug will usually do it, but check them often.
Once I think I have them all snugged up, I'll spin the wheel and hit the spoke wrench on the spokes and see if they all sound the same as they pass by. If you still have a loose spoke, you'll be able to hear the difference in sound. It's a good idea to check the air pressure and spokes every time you ride.
The last trick on the play bike wheels is to run a rim lock. This holds the tire in place and keeps it from spinning the valve stem out and popping the tire. All you have to do is drill an extra hole in the rim and install it when you are changing the tire the next time.
Hope this keeps your wheels alive and you on the track!