Start with a square (cardstock is best). Fold the square corner to corner so that you see 4 triangular sections. Cut the bottom in two on the fold and overlap. Glue or staple. This forms the base or foreground.
Have the kids color in the background habitat scene. Add a few cut out dinosaurs with stand up tabs. Or, of course the kids can draw their own. Volcanoes and nests filled with dinosaur eggs are a must! Kids will LOVE these when completed.
The following link is a great template for a triorama. Check it out!