Here is a helpful article for parents in your situation:
The author recommends that parents opt their children out of mindfulness meditation programs for religious reasons. The presenters may say that the program has no religious content, but you can respond that the program is against your religious views anyway. (Mindfulness itself is a Buddhist concept: it's one step in the Eight-fold Noble Path of Buddhism.)
As a point of concern, quite apart from religious issues, I wonder if the teacher is aware that some people may suffer from negative emotions or traumatic memories when they engage in mindfulness meditation. See, for example:
In an average classroom, it's likely that 10-20% of the children have suffered some kind of trauma: most commonly domestic violence or sexual abuse.
- How prepared is the teacher to recognize when a child is having a negative experience during meditation exercises, let alone take some appropriate action?
That really is a situation that calls for a trained therapist, and it is not right to expose children (who cannot meaningfully consent) to the risk of such a reaction, especially in a group, in front of their peers.
Finally, here's a piece (even from the liberal Huffington Post site) about meditation as a stealth way of putting Buddhist practice into schools:
I hope this all helps.