Children, teens and young adults are unfinished. Their brains develop from the bottom brain stem up and they aren’t completely mature until sometime in their early twenties with the most complicated part — the higher order, impulsivity and regulation part — finishing last. When they are younger they literally rely on our brains to bridge the gap. When they are agitated or angry the best thing we can do is stay calm so they can borrow our calm. Just like we help them by tying their shoes until they can tie them, we help them by loaning our regulated brain until they can regulate.
Dan Siegel has a great video about this; I encourage you to check it out before you finish reading this post: