For the really young ones I take (12-18 months), I usually do a quick phone call/email right at the start of nap. It is just a check in as I have found most anxious parents like to hear my voice right at the start of things and it makes them feel better to hear that they are sleeping. I don't usually mention diaper changes unless they had like a big bowel movement or seemed blocked up. I know they trust me to take care of their littles, but sometimes it is just nice to hear that they are fine. I do this until it seems like I am bugging them at work and then the phone calls/emails taper off. If they asked about it, I would start up again but so far no parent ever has. By about a month-ish, they seem to get the picture about the day and are happy to wait until the end of the day for us to chat.