Aggrsive behaviou-growling

Question
My 12 years old male, neueter Black Lab (Brett)  has started to grow to one of my grandchildren.  He has done that before to other members of the family. Recently, my son,his wife and two small kids (4 and 1 yrs old)moved in. Since then, Brett has change his mood.  The vet said this cannot be reversed, better to put him to sleep, Any suggestions. I have to go to the extreme recommended by Vet.

Answer
One of the reasons I like Labs for little children is, that they are large, sturdy dogs that can stand having a toddler toddle over on them.  At 12, Brett likely has arthritis and perhaps can't see or hear very well.  Kids can be a painful surprise.  My head supports your vet.  My heart says find another one and get some good painkiller and maybe other medication.  I usually am slow to suggest modifing behavior with drugs, but this isn't the usual case.  In addition to her pain prescription, my 14 year old Lab gets 500 mg of glucosamine a day.  So far I have only had one snapping incident with a little child.  I do push my luck taking her out in places such as festivals.