Peel the banana. If large, cut in half to make 2 pops. If using a smaller banana, slice off one end, if not straight. Poke a lolly stick into the end of the banana(s). Dip into the yogurt, using a spoon to cover the ends if needed.
Put the Grape Nuts or other cereal on a plate.
Roll the yogurt covered banana(s) in the cereal, then lay it / them on a baking tray lined with baking paper. Put the tray in a sealable plastic freezer bag, or cover with cling film and freeze for at least 3 hours, until solid (can be left overnight, or longer).