educate equip enable
The Greek word for children emphasises the relationship. But son emphasises character. If someone calls you a son of a dog, they aren't talking about your parentage. They're talking about your character.
Angels were created, not generated. I can take some clay and create a piece of pottery, but I can't create a son. My son is generated. He has my genetic stamp on him. When we were born again, we took on the genetic stamp of Almighty God as His children. No longer just as created beings like the angels.
How do you know when someone is part of a person's family? There's a family likeness. That's how you can tell that my children are my children - there's a family likeness. It's the same in God's family. When a person is born again into God's family, God becomes their Father, and they begin to take on His characteristics.