I have just returned after driving my kids around. It is now getting dark while kids are still coming home from school sports, after school activities, etc. and I have seen many kids on bikes with no lights. Some don't have reflectors either. They are still weaving on and off the sidewalks, riding on the wrong side of the road, not stopping at stop signs, all bad things to do at the best of times, but in the dark it is crazy.
If your kids must ride their bikes in the dark, and I don't see why they shouldn't if they know how to ride in the dark, then they must be well lit. It isn't just a matter of what the law says, but they must be seen. Front and back lights are a must for safety reasons.
Please, before there is a tragedy.