What are the laws in your In-Laws State per motorcycles?
Then, you are the parent. It doesn't matter what other people's kids do per motorcycles, this is YOUR kid. So YOU make the rules.
Problem 1) Then, your in-laws are giving you another story versus your daughter.
So you will probably never find out the real truth, about it... and if they took your daughter on a motorcycle or not.
Problem 2) Another PROBLEM, with your In-Laws is: if they cannot tell the truth and always ignore what your "rules" are for your child, then you cannot trust them.... with motorcycles and your child, and for other things.
Problem 3) AND-- if your Husband is just invisible in all this and has no ability to speak up, nor for you or your child or her safety, then you have a 3rd problem. If he cannot or will not, step up to them, then you will always have a problem with your In-Laws. And your daughter, too. And she will always be caught in the middle of it all. Having to choose between your rules for her as a Mom, versus what her Grandparents.... do with her.
Problem 4) And, a 4 year old, cannot decide for herself what is best or not.
You can opt, to NOT let your child stay in MO with them. Ever. OR, if you do, then you or your Husband has to accompany her, too. If you do not trust your In-Laws.
That is across State lines. To another State. There are many other things to be concerned about when your child is in another State with your In-Laws, besides just the motorcycle riding. For example.
Like, if your child is with your In-Laws in another State, and she gets sick, or gets hurt or in an accident in other ways, do your In-Laws have consent to take your child to a Doctor and does she have insurance etc.?
Lots of other things, to consider.
YOU are the parent.
You do not HAVE to, let your daughter go visit them. By herself.
And, IF.... your In-Laws are lying, I would NEVER send my daughter over there. AND your Husband, needs to know this.
Is he going to just please his parents... or look out for his daughter and back you up?
And if they are lying about the motorcycle riding, then what else would they lie about? Do they even have car seats, in their car for your daughter, when she goes to visit them? That is another "safety" issue.
My friend, her Dad took her youngest child in his car to go somewhere. He let her son ride in the front passenger seat. He is too young and too small to do this, and per laws. And... he got stopped by a Cop. AND then had to pay close to $100 for being ticketed for it. He did not, have her son's car seat in his car... at the time.
And apparently, her Dad had done this before. But never told her. Nor did her son, tell her either. But her Dad got caught, by a Police, that time. And that is the only way, she found out.
So, that is another example. Of things. Beyond motorcycle riding.