Ref. No. 1076/41-271
In the name of Allah the most Gracious the most Merciful
The answer to your question is as follows:
It is not permissible for a Sunni Muslim girl to marry a Shia person whose believes are based on kufr. Children have to obey their parents and consider their will or opinion. In this way their future would be safe in-sha Allah.
And Allah knows best
Darul Ifta
Darul Uloom Waqf Deoband