When you fold the strip of paper around itself several times and then push the edges in to pop it out you get a pentagonal star. We use gift wrapping paper cut into long strips of various widths. You have to make sure the strip is very even, and discover by trial and error how many times to fold so your star pops out well - this depends from the type of paper used, and the width of the strip. The folds need to be tight. Notice also, that if you fold the paper tightly and carefully, it knows where to go.
Common mistake is to force the paper to fold along a wrong side.
There are different ones for every age. Erick Wong, who last year, at 17, got a degree in math and computing science at SFU, told a Vancouver Sun reporter who intervieved him afterwards that his love of mathematics started with puzzles his mother was giving him in elementary school. There are many good posters available. Start collecting now. Or prepare a list of books, resources and places to get them, to give to teachers and parents.