bearded bragons

Question
Will a boy dragon eat a little girl dragon?

Answer
Do you mean putting an adult male dragon with a baby female dragon?   
Any bearded dragon can and MAY bite and harm another dragon.  This happens with baby dragons among themselves many times.  Also, adult dragons can kill smaller dragons...
Even bearded dragons that have been together since hatching can bite and harm each other.
Male dragons will always fight to death...
and if course...it can happen with females and opposite sexes...
hope this helps!!