My 3.5 year old, 3.5 foot long BP weighs in at 685g. Seems incredibly light compared to your 3 year old. Is that right? I have asked the question on here but was just advised to buy some scales which is fine, but having done that and weighed him, I still dont know if he's underweight or not! I fed him 2 large mice (rather than one) for the 1st time at the weekend which he ate quite readily...