Please be sure to talk to an art or pottery teacher and make sure that the items are needed/wanted BEFORE you donate them.
I work at a community center and people frequently donate things that we simply can't use - we have a limited amount of space for pottery and many things just aren't compatible with our current set-up and needs. Also keep in mind that if you don't want it because it's too old and worn out that we might feel the same way. Yes, our budget is limited, but worn out is worn out. Lots of donated items (and LOTS of molds) have wound up in the landfill because none of the pottery people were there to refuse them when they were dropped off and the other staff didn't know better than to accept them. And these unwanted donations wind up costing money because someone has to be paid to load stuff up and haul it to the dump.
I can only speak for my program, but the only slip-casting molds I would even think about accepting would be small, not explicitly religious items related to holidays - snowmen, reindeer, turkeys, eggs, hearts, ghosts, witches. Little things that could be made ahead and painted as part of a children's activity.