Number of kids and why

Two kids or may be three is a good number. Though, I have just one son, I hope to adopt one kid and if our finances are good, we would adopt two kids. I think, one should have at least two children so that they both have each other to fall back upon. If there will be one kid, he would be bereft of beautiful relationship of a sibling. And there will not be any support structure when he grows up.