Are you a centre or a day home? Most people here are day homes, so to be honest, with Provincial ratio limits ranging from 4 to 6, it's not too hard to just know.

I think in Ontario, your limit is 5 so unless you have a lot of client's on rotating shifts or part time, then I promise, you will just remember that many children.

Worst case, just set yourself up a Google Calendar. You can have several calendar's attached to your google account - We have one for day care and several others for my own appointments/group/hobby schedule and one for my husband too - and you can set the up so the font is in different colours and all merge into one if that's your preference.

I find keeping things simple and not over complicating anything is the best way.

Maybe just a monthly sheet you print off and write expected attendance is all you need.