I do a simplistic daycare log for all my parents till their child is 2, or they (we) decide its not needed anymore...if its too repetitious, etc. But often they do use it till birthday #2 (as long as I offer it). Mine is super simple, like a time card.
I do know of other daycare providers who do it in a notebook, so parents write stuff overnight too. (all ages of children). She even ended up with it written into a parents divorce decree..that this had to be filled in and go back and forth, so the parents were all "on the same page" with what was going on...basically so the parents didn't have to talk to each other.
With twins, I don't think its unusual..to know who ate when and how much..when they had dirty/wet diapers and when they slept. With a singleton, much easier...but even with my daycare..and 2 similar age, unrelated infants...its ALOT harder without it written down!