Personally...Id build a 7 ft rod..2 piece..and a 3 wgt and overline with a 4 wgt line. If the child can ever learn to cast a 6 1/2 ft rood...doing a 7 ft wont be any problem...and if you build it "right"...later on in life they can always use it as a small stream rod....should they advance up the ladder in fly fishing.