Quick Sand Scene

My initial thought on this would be to put a tarp (or something similar) down in the area you are going to put the scene. You can cut the tarp in an irregular shape, if needed. Get enough bags of play sand or leveling sand from your local hardware store (Lowe's, Home Depot, etc) to cover the tarp. Arrange various arms, legs, etc. in the sand to give the appearance of sinking victims. You can make the bed of "quicksand" look more natural by arranging plants, rocks, or other materials around the edges.

yes, a tarp for sure, or take a few extra extra large trash bags that are black ans split them. you can use rebar or whatever to have stuff sticking out of te ground

You could also use a kiddie pool. Make the area look as though it is not on a "rise" fill it with sand and water to make more of a Muck and have the parts hanging out....

I saw somewhere where the had a safari hat on the ground where there was a sign that said "Quick Sand - KEEP OUT!"

Last year in part of our haunt we did a playground scene for the kiddie area, where nothing would pop out and scare them. We had little zombie babies on swings and on a jungle gym and some playing in a quicksand box. I made a square wooden frame, laid a black plastic tablecloth under it, dumped in some sand and had the dolls sticking halfway out of it. Kinda cheesy I know but it was a big hit.