The definition of God and infinity are different. No God necessary for infinity to exist.Do you understand the cosmos go out in each direction and go for infinity? Our little universe is just one universe of an infinite time and space.
Think about just our universe. OK? Put it in a box in your mind. Got it? Now what's beyond that?
Even if you believe in God, are you really putting God inside a box? You're saying God can't go somewhere beyond our little universe?
If there IS anything outside the cosmos (we do not know this)... then God also create that. I don't see where anyone has limited God to just this one universe. God is also not limited to only creating life on Earth.
But I would like to go back to another statement you're making... what is infinity? Give me the math formula to calculate the value of ∞. If you cannot define the value of it, then you cannot measure it. If you cannot measure it, you cannot test it. If you can't test or measure it, you simply can't apply physical sciences to it. Infinity is not a physical property. It can only be imagined in a philosophical (spiritual) context. If you believe in "infinite time and space" then you ostensibly believe in God. There is really no difference other than the language you're using to define it.
God has other children? I feel like a family that finds out daddy has another family in another town