We have seen our own parents go from invincibly strong protectors to people who may need care themselves. That gives us a sense of obligation to our community. We have gone from consumers of tax dollars to providers of tax dollars. The town that provided roads and schools and medical care and clean water, when we were growing, now needs us to give back to it, with our taxes, and with our volunteer work, so that the community will work for our children. We have gone from protected to protector, assuming responsibility for those who are unable to fend for themselves.
Altruism is an adult concept.
It is adults who teach children to share their toys. As adults we share our own toys by building playgrounds for children, preserving the community's art and history, creating symphonies and theatres and libraries, raising money to fight disease. We put our knowledge and stores of data on the internet so that other people can use it too. Adulthood brings with it perspective. Babies who are hurting have nothing to gauge the pain by, and all pain gets the same howl of indignant protest.