Prayers up.
Make sure he didn’t throw them away on purpose. At his age I was starting to notice any differences between me and the other kids and I can tell you I would’t have been above chucking them down the storm drain (the most forbidding, mysterious place I knew of) if I didn’t like them.
I had a friend whose son was 6 at the time and he threw his shoes away because they "were ugly and didn't look like the other boy's shoes"(his words). So one day he comes home in his sock feet and no shoes. He said the tried to wear them out but they were to tough so he just tossed them. He didn't do it again after the tanning he got.
I second this. You are so right, five is the age where they begin to want to fit in. As well as the age of total absent-minded bliss. Their little minds are always elsewhere.
I made my folks crazy losing and breaking expensive glasses. Often outside, actually very often outside. Toyboxes, any kind of box, under things, especially under things you wouldn’t think you could put a pair of glasses.
My prayers and best wishes.