I use a knot that is used by most Russians to tie their shoes. It goes by many names; Seaman's Shoelace Knot, Double Slip Knot and, Ian's Secure Knot.
It has never failed me and is not all that difficult to teach kids.
Here is a link to
Ian's Secure Knot.
Here is the start page so you can see all of
Ian's shoe-tying knots.