G-d’s eternity

Why does G-d live for ever? [Nathan aged 8]

You’re right when you say that G-d lives forever, He is Eternal as He always existed and will always exist.
Because G-d created everything in space and time, He cannot be limited in space and time, He is above it and that’s what we mean by being Eternal.
If He wasn’t Eternal that would mean He would be in some way finite – limited and lacking in power which cannot be because we know that G-d is all powerful. [Children's Rabbi]