This might sound like mushy sentimentality, but there is some actually hard science behind it.
People who marry, and have children, tend to live longer than those who stay single and do not have children. People who stay married tend to outlive those who divorce. That's not an absolute. It's not to condemn people who don't marry or have children to shortened lives. But it's been found to be generally true. At the same time, another group who often live long lives, are nuns.
You've got two extremes there. People in relationships which produce children, so they involve being sexually active; and those who have no intimate physical or romantic relationships, and don't have children.
So what do they have in common? They both put a great deal of their lives into caring about others. Caring about other living things is a kind of loving - not the romantic sort with melting moments in the moonlight, but to give and care about another is to love them. Marriage involves certain stresses. So does having children. To keep a relationship going and raise children well you have to care about someone apart from yourself and put them before you at times. In a different way, the nun's vocation involves giving her life over to the care of other people. Despite living in quite opposite ways, they both have to extend themselves to be there for those around them instead of just doing their own thing and pleasing number one.
This is not a critisism of people who divorce. Members of my own family have been through it. A person's marriage might end without it being their fault. A divorced person might still be a loving and giving individual. The general trend, with exceptions, is that living longer happens for people who have a relationship which involves caring for others - and having someone to care for. Come to that, keeping a pet or companion animal also seems to be good for people. The same applies. There is a living creature there who needs your attention, and needs you to do some giving.
That could be for a several reasons. If you have to care about someone else, or something else, then you have less chance to dwell on your own issues and let them get you down. Also, if you want to be there for others, you have a reason to keep going. Part of survival is the will to live. You have a will to live if you feel needed.
It sounds corny and mushy to say things like 'It is more blessed to give than to receive', (groan, roll the eyes) but some things are true even if people trash and ridicule them. If a cynical or miserable person can't see that, it may be tragic for them, or it might be they should quit trying to spoil it for everybody else. The thing is, it might be FACT that a human mind and spirit get stronger and their health is better if they give, instead of just trying to take.
Christmas, or family times like it, can be great when you're a kid yourself. They can lose their sparkle for adults, because they get 'same old, same old' and they mean having to be polite and putting on an act; then they can become exciting again when you have children of your own. Kids opening their Christmas presents can be a real ball!
When the strain gets to you, it can seem that having children involves a load of trouble. But when you see the good side, then it's 'everything old is new again'. Our kids loved making mud houses in the yard, going to the zoo or fauna reserve, ridng tricycles and bikes, hiking, going to theme parks, having rides at carnivals, all the things we did - but for them it's new. You can catch the mood from them. Recall taking children to the movies. They loved it. And it's fun when they're having fun. Life renewed. I can remember when our eldest boy went started school, hoping it would be good. I recall taking our daughter to her first ever dance, worrying how it would work out for her and being glad when she enjoyed it. The same goes for things like teaching them to swim. Later, it's teaching them to drive. The point is, they need you. You make yourself live up to it. It'a a way of 'getting a life'. You don't live THROUGH your kids, if you do things the right way. But if you live FOR them, you've got more to live for.
The same goes for your spouse. I don't depend on my wife, or she on me. It's just that there is a lot more to live for if we've each got each other.
Could it be that our species is made that way? It is good for your heart and lungs if you exercise them. In the same way, is it good for your spirit if you extend it to others?
It might sound like mushy sentiment, but what if it's real? To care for others is good for yourself. That might be one of the most important ways that humans are made in the likeness of God.