Hi Bears
I saw your question early this morning and was hoping that someone would come along and post a reply.
Your son asks a question which is very common for young minds (and probably for many older ones as well).
My thoughts: From the perspective of the Bible, we understand that God always was, is, and always will be. He is not restricted by time, as He created time itself. He is eternal and thus always existed, as He exists in eternity, apart or outside of time (and space). He is the great cause of the “beginning” and the “sustainer “of all that comes out of, or, from that beginning. In other words for a young mind “He was always there, or always existed and will always be there”. We know Him as the self existent One.
As we are created by Him we are finite and understand that we had a beginning. But He is infinite and was before any beginning and will always exist into the future, even after time has run its course. Thus He is from everlasting to everlasting. In such a God we can have complete confidence.
In the Old Testament, God reveals Himself through the various writers by several dozen self contained names (most often translated as God or Lord). Each name of God, helps us, with our finite minds to comprehend an Infinite person .... Himself. Each name represents one side of a multi-facet diamond that is absolutely beautiful, almost beyond our comprehension. One of those names is El Olam, meaning, The Everlasting God, The God of Eternity, The God of the Universe, and The God of Ancient Days.
EL is one of the names that is often translated as "God" and can be used in conjunction with other words to designate various aspects of God's character. Olam is derived from the root word ‘lm (which means "eternity"). Olam literally means "forever," "eternity," or "everlasting". When the two words are combined - El Olam — it can be translated as "The Eternal God."
The first time this name of God is used is found in Gen 21:33 – “And Abraham planted a grove in Beersheba, and called there on the name of the LORD, the everlasting God.”
The Lord Himself encourages us in the New Testament to bring the younger ones to learn of Him ...
Luk. 18:16 But Jesus called them unto Him , and said, Suffer little children to come unto me, and forbid them not: for of such is the kingdom of God.
Young children are very keen on learning about Him and can often ask the tough questions. But also they are often able to easily accept and understand the answers.
I do hope these thoughts are of some help. :-x
Andrew