We took our BIL's (DH's brother) 3 kids one long weekend to give him a break (he and the kid's mother are separated). We were insane - they were 3, 4, and 5 yrs old at the time.
But it was nice - we didn't have too many problems - the youngest gave us the hardest time during naptime and the 4 yr old - well she got really pouty for awhile. It was 2 boys/1 girl.
Bathtime was fun - DH did the boys, I did the girl
We got them to help make cookies and they wanted the dough more then the cookies. Our best times were "reading before bed". We let them pick out the story book.
Not sure if we will do it again - we are NOT used to little kids and we won't babysite babies - that was the requirement to watch the BIL's kids - all of them had to be potty trained!