The short answer: we don't know yet.
Slightly longer answer: as of April 23, 2016 we don't know. It's certainly a valid question. In the books when Bran reached what seems like the last bastion of the children of the Forest, they did seem to be fighting the White Walkers. The setup seems to be that they don't particularly like Men, but they can survive where Men can not and so simply coexist and do their navel-gazing.
In contrast, the White Walkers seem to want to bring a tide of death over everybody and everything. Thus, whether Men realize it or not, the Children have made common cause with them.
But even that said, the Children seem to mostly ignore the White Walkers and go about their business of... tree stuff. So perhaps it's simply misleading. There's no real way to know.