No but your actions can cause some problems for your husband in court. You have no legal relationship with the children (unless you are one of the very few who the courts have extended such to a step parent).
What you are doing is causing problems. There is no real reason for you to be there and you know that being there causes problems.
The fact that you are asking if being on the sidewalk is trespassing shows that you want to prove you are right and can do what you want rather than minimizing the problem. Since you are willing to cause an argument that you know the police might be responding to, what do you think a judge will say about how your husband is caring for his children by allowing you to instigate such a confrontation?

