How Can I Best Explain the Holy Trinity to a Child?

You don't have a chapter in the Bible that is an explanation of the Holy Trinity - you have a formulation of that. The reality of the trinity is born out of just viewing things, so it's a hard one for a child. But that is the importance of catechetical teaching, in that we explain to our children that God is three in one and one in three.

For me on this subject, see the following articles:
How to Explain What the Holy Spirit Is
5 Scriptural Points to Help You Understand the Trinity
How to Explain the Trinity to Children

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