Tightening the bolts on training wheels for a child's Schwin bike My child is learning to ride his first bike and I have attached the training wheels to help him learn to balance.  I have adjusted them to be slightly off the ground so he can get used to the feeling of balancing.  My issue:  The wheels simply won't stay in place for longer than a single ride.  I notice that as my son rides and the wheels take his weight they slide up and then he risks falling on that side..

Beyond the risk of over tightening the bolts using an electric tool is there any other method of ensuring the wheels do not slip?
Simple answer - do the bolts up tighter.

Bolts for training wheels are pretty hefty, it's hard to over tighten them with a hand wrench. 

If you don't have a suitably long wrench that will allow you to get the torque you need, you can extend the wrench handle with a length of metal pipe. Avoid using an adjustable wrench as these can round the bolt heads off. Not everyone has a length of pipe laying around of course. Any good bike shop will tighten the bolts for free or a nominally low charge.