All perfect praise be to Allah, the Lord of the Worlds; may His blessings and peace be upon our Prophet Mohammad and upon all his family and companions.
Allah Has Permitted Muslims to eat the meat of animals slaughtered by the People of the Book if the animals are slaughtered according to the Islamic form through a cut to the jugular vein, carotid artery and windpipe, even if Allah`s name wasn`t mentioned while slaughtering.
Some Christian countries slaughter animals according to the Islamic form while some use electric stunning. Thus, your son must ask about the method of slaughter. If it doesn`t violate the teachings of Sharia, then eating that meat is permissible.
It is worth reminding that it is permissible to eat fish regardless of the one who caught it. Similarly, it is permissible to eat eggs regardless of the chicken owner. If your son has doubts about the method used to slaughter the animals, then he may suffice with eating fish and eggs.
We pray that Allah protects your son and all Muslims from falling into sin. Indeed, He is All Hearing and Answers the call of those who invoke Him. And Allah The Almighty Knows Best.