Forgive me for not so good english
First of all, you should tell us, what was the shutter speed that you had in given conditions.
Next, I am not sure from what direction you were shooting. If your kid was sledding directly towards you, I think you should put IS mode to 1, not 2, so that stabilization could compensate for vertical and horizontal movements. 2 is for panning, so that compensation is not affecting horizantal movement.