If they both are truly 3 years old, then yes, I would say that they are severely underweight. I have a 1 y/o that is 600grams, a 1400 gram 2 1/2 year old female, and a 1100 gram 2 1/2 year old male, and a 2,200 4 1/2 year old male. the 2k gram male gets 1 med rat aweek, and everyone else gets 1 small rat a week. just a qeustion, how long are your BP's because they might not really be 3 years old