I keep daily logbooks but they are for my reference, what children like or don't like to eat, naptimes and diaper times so that when we get to toilet training I can see if there is a pattern for poops and I can get them ready for the potty at that time. But I have always given the parents a verbal update at the end of the day.

I have one picky eater so her Mom asks me to send her an email every day at naptime with my daily menu (nobody else has every really cared about the menu) but this little girl won't eat any food in the evening if she's had it during the day. The Dad isn't great with messages, hehe and does dropoff/pickup so it gives me a good chance to keep an open communication with the Mom.

I wouldn't want to have to write out elaborate paperwork for parents, they wouldn't read it anyway, just a nuisance to them. And I have clients who don't check their email regularly so that wouldn't work for all. Find the system that works best for you and your clients.