tough choice, I personally prefer the Encore in rifle configuration. The Contender is too light for me. But then, you're getting for a little fella. Last summer I had to consider the same options for my son, who isn't a whole lot bigger than your little guy. We chose a Contender carbine and picked up a 21" 6TCU from VVCG in one of their Wilson blank sales. Even though it's a bit light for me, this is one sweet shooting combination. My boy took his first buck with the TCU, a little eight-point that I just had to get mounted for him.
Consider the 6TCU.
Rick