All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Arguing the matters, which still do not occur, is not recommended. But a wise person never makes presumptions a means to break his relations or to put an end to his good ties. It is very possible that one may not get children at all or if he gets them, they will be on the right path, Allah willing.
However, disputing before their coming into existence is too early. The husband's claim that he will do so and so, if they become non-Muslim does not justify seeking divorce from him.
As for the ruling of Muslim children who apostatize, it is necessary to give them time till they become pubescent. After that, they will be demanded to repent and adhere to Islam. If they deny repenting, then the ruling of an adult apostate applies to them.
Know that only a Muslim ruler is eligible to carry out those rulings, not fathers or someone else.
Allah knows best.