Children often ask this. The quick answer: God wasn’t made, He was always there. Only things that weren’t always there have to be made.
But atheists may still complain about God being used as an explanation because it stops inquiry. We should always look for some other explanation because of this. Saying “God did it” stops science. Sometimes they also insist that to use God as an explanation, we need to explain God first.
I think these complaints are based on a confusion between arguing that and explaining how. When theists use God as an explanation, they are arguing that. That is, they are trying to argue that it is true that God exists and did such and such. Theists have to admit, however, that this does not explain how. It doesn’t provide details about the processes of how the universe was made. Because “God did it” doesn’t explain how, atheists reject God as an explanation.
But we can use explanations for both of the above purposes. We can use an explanation to uncover a mechanism, or we can use an “inference to the best explanation” to argue that a certain event occurred. An example: I can explain why the sky is blue by pointing out different features of light and the absorptive properties of gasses in the atmosphere — that’s explaining how. Or I could argue that my friend was awake late last night because there is an email in my inbox from him with a timestamp of 2:20 am. In the latter case I am not trying to get into the details of how the universe works so much as show that my friend was awake at that time. Notice that I don’t need to have an explanation for why my friend was awake to make the point: what kept him up is a different question from whether he was up.
In the same way, when theists offer arguments for God’s existence involving God as an explanation, they aren’t trying to uncover mechanisms that can be used to further scientific inquiry. They are merely arguing that God exists; they are arguing that, not explaining how. And just like my friend’s email, arguing that God exists isn’t the same as showing how God exists.
So arguing that God did something may not advance scientific goals, but that in itself doesn’t mean that God didn’t do it, or that God isn’t a good explanation. It just means that God doesn’t suit the goals of atheists.