On one of the days of Ramadan, I kissed a small child on his mouth. My question is: I do not remember whether any of the child's saliva entered my mouth or not, and if it did enter my mouth I think it is most likely that I did not realise that this action breaks the fast, because I think that if I had known that I would not have done that action. Do I have to make up those days?.
Your fast is valid and you do not have to make up anything, because you are not certain as to whether you swallowed any of this child's saliva, and an act of worship cannot be invalidated in the case of uncertainty. Even if we assume that you did swallow some of it, you do not have to do anything because you were unaware that this invalidates the fast.
And Allah knows best.