Boil pasta (spaghetti works well) or rice in pots of coloured water until cooked but firm. Drain and allow to cool to body temperature then give to the kids. The sticky pasta usually needs no glue, but you can make the cornflour glue for them to use as well. (which will make the creations a bit more durable)
Dried pasta with holes (“penne” for example) works well as beads for stringing.