Yarisugi!
And even though you managed to get the desired look without corneal damage, using hair dyes on very young children increases the risk of their developing a hair color allergy later in life. The worst case scenario would be, if the kid actually likes the look and decides to repeat it when he is old enough to decide for himself, he'll get contact dermatitis, or worse, an anaphylactic reaction every time he retouches his roots.