DD2's teeth were a bit crooked at first, but they straightened as she got a bit older, around 2-3yo. Now all three older ones have hillbilly teeth they are all shockingly crooked and DS1 and DD1 had perfectly straight teeth as toddlers so I don't think there are any real rules about it kwim? I can see a lot of money being spent on dentists in this house in the next few years