I work with kids, don't have any of mine own but have you tried giving them a colouring book or something quiet to to like look at books, toys that don't make noise etc... How old is the kid? Any 2-5 year old will feel important if you sit them at a table with u and some paper, and tell them by drawing they are helping you.
Fail all that a video or kids CD like hi5/wiggles etc keeps them entertained.