I’d say a principal would only absolve you of responsibility for your space if THEY could honestly tell you that they have no other space in which to store the furniture. Talk to the custodian first and ask if s/he knows about the furniture. If not (they should), ask the principal. This especially if you don’t use the furniture at all. Explain to the principal that it is in your way / taking up usable space (if this is true, which I assume it is). If the principal admits that there’s no other possible space in the school for the furniture, then it is of course your responsibility to make sure that the kids don’t touch it.