Maybe 10.
Or
Anyone who has been attacked by ninja toddlers in the night knows to watch their back, as they are sneaky. They feel no remorse jumping you, demanding a piggy back ride, when you least expect it. As I am myself – by birth – part ninja/part hero I am not sure what to expect from this showdown. My strides are cat like and soundless, and I could probably pass without detection. Also, I know by heart and disciplined training a variety of ducking moves.
Would I be detected I would assess the situation, give it a power pat-down, and after eye balling eachother, exchanging mortifying looks, I would commit to the fight with no fear.
However, knowing that everything involving children can be solved by a ball, I would suggest throwing that in one direction and shooting for the other.