Children are resilient and they will adapt whatever their norm is. I honestly couldn't imagine my parents together, I can't remember them together. But then my god children can't imagine their parents together now either and they were 12, 10 and 6 when their parents split 10 years ago, they are happier than they were when their parents were together.
What matters is how you do it how amicable you are, at least in front of the kids. Handling it positively, age appriote conversations about what's going on, making sure they feel loved.
And also tbh if your not happy and your sure it's over get the hell out. Please don't stick in an unhappy marriage "for the children" your children will know your unhappy, it will concern them. The resentment and anger will grow between you and your husband and it will lead to a messy divorce.
As for why it's harder as adults, if you base your whole life on the thing you think is secure and safe, the thing thats consistent, your parents being together and then suddenly they divorce, everything you thought was normal is brought in to question.
As we've all said and implied children are resilient, they'll base their norm on mum and dad not being together. They are much more able to do this than teens or adults