It is not so much an inference of A to B in modus ponens since an inference would be coming to a conclusion not directly supported by the facts. In the form of modus ponens the argument is only controlled in that

If p then q. p, therefore q.

This argument form is the simpliest in form and is only valid for that condition. Granted children pick up on it easily enough for

If they behave they can go out and play. They behaved, therefore they can go out and play.

One could say that basic logic in this form is "Childs play".

Now, Modus tollens is based on inference as a whole line of events can cause the argument to be valid like you mentioned. Since these events are not addressed directly the argument for is valid. We look for examples disproving it, none of which are addressed in the conditions so they of no consequence.

If p then q. Not q, therefore not p.

The argument for is simply but it does not establish a definitive cause and effect for validity.