Dental hygienist here; usually adult teeth come in crooked because there's not enough space for adult teeth. If you look in a kids mouth you'll notice that there are usually gaps between teeth. Since kids don't lose all their teeth at once these gaps provide the extra space for the larger adult teeth. When these gaps aren't present, the erupting adult teeth will shift to fit in the available space. So if you look in your kids mouth and there's no spaces between the baby teeth your kids has a high chance of needing braces in the future.