I'm sorry for what happened to your son but all terriers should not be tarred with the same brush!
I have 3 dogs- 2 of which are terriers, Mika my yorkie and Nikki my staff (traditional staff not amstaff). I also have 4 children ranging in age from 1 1/2 to 11. Neither of my terriers are territorial in the slightest-anyone (including my kids) can take the food out of their mouths without even the slightest hint of aggression. Neither terrier has ever even growled or snapped at anyone,ever! My Staff is 6 years old and we have had her since she was 6 weeks old-she has had 3 litters of pups and anyone can go in with those pups from the minute of birth and she is just sooo pleased to see them and never displays any aggression. (I don't allow everyone in by choice, but she really does not mind) If someone were to break in our house I'm afraid my 2 terriers would greet them like long lost friends my sheepdog on the other hand might be the one to protect us and our home (although he is totally soft and gentle with those he knows). Mika is an absolutely sweet and adorable little thing and rarely barks (I mean very rarely-she's practically mute!) Infact all 3 of my dogs are quiet and they do as they are told-immediately. Good training is essential and its true that terriers can be strong willed but my will is stronger
and my dogs know that they are at the very bottom of not just our family pack but under anyone that we bring into our home!!!