Well, unfortunately Mormonism is a way of life for their cult members. You should explain to your kids that this is what THOSE people believe, and this is what Mormonism is. We don’t subscribe in our family, but we don’t persecute others for their delusions lol I mean beliefs.
The Belief Book is a great place to start: https://www.amazon.com/gp/product/B07LC24GTF?ref=dbs_p2d_P_W_kindle_available_T2
It might be a hard knock growing up for your kids as the Mormon kids are going to exclude them sometimes and they will feel left out when their peers are getting baptized and celebrating (not because of the religion but because kids want to belong), and they may be curious. You’re a good parent and you see religion from an academic point of view which is always the way to explain things to kids. Remind them that Mormonism is just a religion and belief system and doesn’t mean they aren’t good or are missing out on something if they’re not part of it. They’re perfectly good kids and no one can tell them otherwise based on whether they go to church or not.