This happens every so often. I have just had my 76th birthday and remember people deciding to have less children, sometimes none, way back; then later on started settling down later and consequently having less, or none. There seemed to be subtle encouragement for this trend, eg some popular television programmes featured married couples without children, 'The Good Life' for example. The feminist movement too, which I fully supported. Women were always worth more than being housewives and mothers.
Meanwhile there were also people who had more than two children.
It all balances out eventually, I wouldn't worry.
Some families seem to be thinner on the ground, others don't.
I grew up with a mother who was the youngest of ten, my dad had two younger siblings. I had loads of cousins but they all drifted away. Most have died now, their kids have scattered. My son (46) doesn't know any now, it doesn't worry him, he has plenty of friends and a good social life. I only had one child but had intended to have more, other things intervened and I don't regret it, we were happy but sometimes I think it is sad that, for all intents and purposes, when I am gone he'll have nobody of his own flesh and blood that he knows. He doesn't seem bothered, has plenty going on in his life.
That's just how it is, nothing we can do about it. In a few years life will be different for everyone, there will be another trend.
Family gatherings aren't always wonderful, we tend to look back with rose-tinted specs, forgetting the stresses and the arguments.