that would really bug me! were the spares still there? Or have they been taken, if so that would more than irritate me,
Label everything with marker pen so it cant be removed and tell the leaders to watch out for stuff being swapped by accident, then when someones caught stealing its dealt with,
my sister (4) had spare shoes and a coat stole from playschool, the mom had the cheek to send her child in them the next week, we calmly removed them from her peg and took them home, some people have no shame!
I would be annoyed, and would worry that the nursery will now think I am not a good mummy for not putting them in there in the first place! I would explain that they were in there, and ask if anyone has taken them out (in a calm and polite way, of course!)