Liz,
There are a couple of things the parents can do to collect urine. First thing in the morning have the child stand-up in the bathtub and run warm water over his feet. This often triggers urination. The parents can then hold a collection cup under his penis to collect the urine.
The other option is to get some urine collection bags from a medical supply store. This can then be applied to the groin area before bed and collected in the morning.
I like the first option better as it usually works quite well.
Sincerely,
Dr. Woeller