Another way to look at this is:

Simon’s problem may be that he doesn't know how to find his snack and therefore doesn't believe he can find it..... ever. This is why the panic - if I don't find it right away I'll never find it since I have never learned how to search.

Try this, next time instead of finding his snack for him (mom is the only one who knows the snack trick) help him to find it himself ( look mom just taught me the snack trick). By talking him through the process several times he will not only discover that he can find his lost snack but he will have the tools to thoroughly search for other "lost" stuff. JMO