iPad with kids / parental controls / reading at night

I have two children that I would like for them to be able to use their iPads to read books on at night at bedtime. The problem is that they are using them to play games, watch videos, surf the internet and so on. Is there any way to lock down the iPad at bedtime so the only app that would work is Kindle or iBooks? It can either be done manually or on a schedule.