Don't be afraid to give them something with a little meat on the bones-- kids don't like to be fed a load of crap or pap, and really kiddie-oriented ones will only appeal to really young kids-- more likely you'll have a mix of ages and some of them will be way too cool to go for little kids' stuff. What you want in church outreach to families is to hook the parents, anyway.

The suggestions above come out of our own weekly service and have gone over quite well. I'd say with the short time you have to work it up, stick to your genre of most familiarity and go for the ones you've heard if you don't happen to have all of them in your repertoire. Mug 'em up, play with dramatic pauses and eye contact with the kids. Oh, and used congregationally, the usual instrumental breaks don't quite work.

And seriously, the kids will want to plunk a string or two or come close for a real good look. The parents will find this very disturbing and try to control the kids' fingers, but what I do is just keep a ratty old autoharp out they can absolutely not hurt at all, and help the parents understand that their kids will be very, very careful if they leave it all to you to manage.

Don't have TOO much fun, now! :~)

~Susan