I'd save the miles and stick it out. It isn't a long flight, all the IFE you are going to get in J you have in W. You get fed marginally better if you upgrade but you might as well spend $25 on some snacks at JFK in the morning.

And at the end of the day I would much rather fly JFK-LHR in W on a dayflight than in J on an overnight, especially with kids.