Actually, I'd argue that parents acting on behalf of or in protection of their children are also acting selfishly.
Hmmm YOur reasoning please
Every action we take is to produce something we want. If I lay down my life to save one of my children, it is because the end result is something that I want.
There are also arguments that altruism in terms of one's own children are based on a biological instinct to preserve our own genes and propagate them in the world. To make sure that "I" live on in my descendants.
Placing the needs of one person above your own may seem selfless, but why are you doing it? Is virtue for the sake of itself possible, or are those who do things like that doing it for the feeling of virtuousness that it gives them? I'd argue that in the end, they are producing a result that they want, whether it's that feeling of virtue or for someone else to be safe or happy. I like giving things to my family because I genuinely enjoy seeing them happy. Is it their happiness or my enjoyment that is the real reasoning behind it?
I'm not saying any of this is a bad thing. I think it's a human thing.