A.C.
I think taking them to things like registration might be ok since you just need to take a few minutes to do it (at least in my previous experiences), but an appiontment with your advisor might be more difficutlt unless they will sit quietly. Do you have a friend you could ask to help out and then offer to watch their kids while they do something another time - a swap like that is always great. How about a parent/grandparent who might be able to help?