I am an adult who has read the whole Bible over 50 times, in many translations and languages. I really do not understand the KJV. The grammar is very different, often it follows Greek or Hebrew word order rather than English, and there are so many obscure words, or words that have changed their meanings.
Why would you inflict that on a child? Get a Bible that they can understand. If you want something more stilted, but also more modern, try the ESV or NASB. I don't like the NIV for unknown reasons, I have read it 2 times from cover to cover. There really is not much wrong with it, inspite of what KJV Onlyist will tell you, but it is a bit too modern and flowing for me. However, if I was giving a Bible to a child, NIV or ESV or NASB with no footnotes, so they can just read. My first Bible had chain references, and it was enough.
If a footnote tries to explain something away, that is not a proper footnote. It should talk culture, (including other nations habits and practices), exegete the word in Hebrew or4 Greek, or otherwise explain deeper, what the word means. I was amazed at the footnotes in my NET Bible in Leviticus. I didn't totally understand the OT references to the atonement and the footnotes explained a lot, and made me dig deeper. I had a footnotes NASB, and it would just repeat again what the verse said. That isn't much help, either. NET also updates the translation to modern English. Phrases that are very normal in Greek, like "he answered, saying..." or "Therefore, but.." which is also saying the same thing are not good English. I agree with the choice, but there are literally thousands of those small changes, and the NET makes mention of every single time. I think that is over the top, although it is accurate.