We ask and 26 voices will ask back....
"Miss, will you look at mine for me?"
"Miss, he/she has my jumper" (they don't, they have theirs)
"Miss, I can't find mine!" (search commences, turns out child didn't bring a jumper with them that day)
"Miss, I have two jumpers" (neither of them their own)
"Miss, let me tell you this long and convoluted story about jumpers which will end in me telling you that I've lost my jumper"
"Miss, I need help putting my jumper back on"
"Miss, I need help taking my jumper off so I can check it"
There are reasons why it's not done and the super simple solution is for parents to use their commonsense and not send expensive items in the first place.
Small children lose things, they spill things, they get messy, they get dirty, they slop their dinner. Don't put fancy clothes on them when they're in a setting where they'll be expected to be as independent as possible, keep for them for outside of school where the parents can give them all the 1:1 support they like to keep clean and to not lose items.