The 940's are good all around tires for Mx they are as lite or lighter then other tires and hookup great out of the corners. For rough tracks they do bounce alot more, this may be a problem for the little guys.
The new ITP tire weighs a little more, hooksup good and does not bounce as bad on the rough tracks it is a great tire for the 70's & 90's I would stick with the holeshot tires for the 50's just because of the weight.