Here’s a story of how I explain the Holy Spirit in us to children. I take an empty glove and tell the kids that it's a magic glove. I tell them it is amazing because it can pick things up. Then, I drop it on a hymn book or Bible and tell it to pick up the book. When it doesn't move, I apologize for its failure and assure them that I've seen it pick up books before. I suggest it might be too heavy, so I move to a smaller book. When it still doesn't work, I move to a piece of paper.
When it still doesn't work, one of the older children is usually on to me and says that I need to put it on. I then suggest that I neglected something important. A glove can't pick anything up without a hand inside it. Then, I share that we can't do anything significant unless the Holy Spirit is inside us. Just as the glove can do things with my hand inside it that it cannot do by itself, so we need the Holy Spirit.
(From Johnny Wilson, Object Lesson: Holy Spirit, 5/25/2009, https://www.sermoncentral.com/sermon-illustrations/72410/holy-spirit-in-believers-by-johnny-wilson)