I have one child who also doesn't nap due to bedtime issues. I was okay with it as she is quiet and will watch tv, read a book, do a puzzle or play quietly. I re-did my contract for the new year and did say in there that each child is required to lay down for at least 30 minutes. I had been doing this with her for about the past month or so anyways and her parents were fine with it after I explained it is my only 30 minutes kid-free I get during my work day. Maybe you could try that?