I would not freak out about one miss dose.

Your son is nine years old. Don’t think that it is time to start having him take responsiblity of his meds? Don’t you think he could remember to take it before he went to bed at the sleep over and when he got up in the morning?

I am glad that you are so close to perfection but, the reality of life is that we are human and we make mistakes. I could see a problem if he did not get his medicine on a regular basic.