Freedom; Is it worth teaching?
I think you are in an excellent position to make a stand. It's not all about the costs. It's about the freedom that is being trampled.
Your response got me thinking. And if I was in your position I seriously would go to the teacher and explain a little bit about software freedom. And after that demand that the templates that the children have to use are in ODF. Or that there are two versions, so people have a choice.
This can be morally (1) and economically (2) justified.
1) FLOSS is about sharing knowledge. Just as a school is too. A long time ago we all decided it would be a good idea to have public education. A level of basic knowledge shared with everyone in society. This was all done to offer children the same chances, independent of their parents financial situation, color of skin or religion. Proprietary software, hinders you to learn from the software. You are teaching children that they are not allowed to know some things. That way you prevent them from taking the software apart and learn from it (as a kid I used to void warranties a lot and that led me to becoming an electrical engineer). So offering ODF as an option, creates a level playing field. It offers a moral choice to the parents. Do I want to teach my children about freedom or following other people's choices?
2) A public school receives public funding. Which means our tax money. If they can save costs, then they are obliged to the community and themselves to do so. Furthermore if they really want to use Office, than you should get a gratis copy. Why should you make costs because they made a choice? Even a choice which you do not support!? Next to that, like KnucklesTheDog said, having knowledge about OpenOffice.org or FLOSS will save society as a whole money in the end. And will give your children the ability to perform a task in more than one way and choose the right tool for it. This is an ability that will make your kids more of value to future employers.
This practice of "hooking them when they are young" reminds me of drug dealers. And we all are addicted to proprietary software. It's time to go to rehab.
You are at the front of the battle ground. This discussion is only for a small part about money, but mostly about the principle that knowledge should be shared freely. The whole idea behind F/LOSS is freedom. The freedom to share knowledge. Once a revolutionary idea when we started public schools and we all know how that worked out. The same thing is already happening for software.
I can only implore you to at least try to get this point across. If you truly believe in freedom, trying to get this point across is a duty that you must not fail to act upon.