Ummm....why would you want to whiten your child?
My kids are rather dark skinned apart from their fair faces, but that's just the way they are. They do receive comments but mostly from family who think it is cute....but if I were to worry about it I dont't think it would teach them self acceptance or help with their self esteem.
Kids learn from us. If we try to change the way they are physically, we are not teaching them about real beauty and self acceptance. Because so much emphasis is placed on physical appearance these days, young boys and girls are suffering. Kids as young as 5 are dieting, 10 year olds becoming bulimic. Teens are getting plastic surgery. What are we as parents teaching them?! Even when we make comments about ourselves - what we dont't like about our bodies, they are listening and learning.
Embrace it. They will grow up accepting themselves and seeing beauty beyond appearance.