Julia had a skin biopsy done when she was maybe a week old, in the NICU. We couldn't figure out what was wrong with her skin, so they were hoping that a biopsy would clue us in (it didn't, ended up doing a DNA test 4 months later lol).
It was a pretty quick procedure, couldn't have taken more than 10-15 minutes, and she didn't cry at all. They did it in her thigh, and gave her a shot of some sort of novocaine for skin (lol you know what I mean). I think they did the "hole punch" procedure, where they literally punched a hole out of her skin; and then they put 1 or 2 dissolving stitches in it. I don't see a scar now, so they couldn't have taken too much.
Goodluck! Maybe bring some toys or books to the appoitnment for your kids.