Until we spent that $170 on a real crimper (which, I need to say, is really worth it), we used to use t
hese pliers from Harbor Freight. Not the jaws, but the crimping die on the handle-side of the hinge. Most kids do not have the hand strength to do a proper crimp with these, so we would clamp the jaws into a vise for crimping and tighten as much as possible.