Remember when you were young, and would make the "baby footprints" on the car window with your hand? Did you do that???
If not, make a fist, and look at the pinky side. It looks like a baby footprint! Then use your fingertip to make the toe prints.
Paint the boys' prints baby blue & the girls' pink, have them write their name beside their footprint, and write "Welcome ____'s Baby Sister/Brother from _____'s First Grade Class, 2009.
I've done this in the past, and this year, I have one of the babies I made a banner for in my class! Her mom told me at Open House that she still has the banner!