M.I.
Since the school is closing, I'm sure the teachers could use some cash. I would suggest collecting $30 to $50 dollars from each family and get TD Bank gift cards (or any gift cards AmEx, Visa, etc.) for each of the teachers.
Cupcakes & cake are always a hit. You could go to Costco and buy a cake with "Thank You for Caring for Our Kids" or something like that. The cost of cakes is so inexpensive, you could get two. If there are children in the class with food issues, you could ask their parent(s) to send something in for them to celebrate with.
You can then send word to all the parents in the class, so some of them can come to celebrate and thank the teachers. Just remember to give the teachers a heads up that you and some parents might come in.