As for the overalls - he may have several pairs too. When I found a sale for my son I often bought more than one. With girls you tend to get more colour choices but for boys one pair of jeans looks the same as the next. If they buy their clothes at consignment stores they may have all been hanging together and the mom just grabbed 5 pair saying ok these will be his daycare clothes. Does he wear a different tshirt every day. Depending on the job of the parents they may need to do laundry daily so what he really has is two pair and just keeps alternating them.

As long as they don't smell and yesterday's jam and the day before's spagetti sauce isn't still clinging to them I wouldn't worry.