First and foremost, the Quran makes it clear that there is absolutely no compulsion in religion. Muslims don't believe in forced conversions. They most likely converted on their own free will, and their parents are just upset. Happens in the US all the time. Christians convert and people closest to them, usually stop talking to them.
Yemen's Houthi rebels commit to peace plan in letter to UN chief, BBC reports (Haaretz)
from the article: Gaza Christians protest 'forcible conversions'