The pattern you describe is typical of children who are on the verge of accomplishing toilet training but who are either fearful around use of the potty or reluctant to 'give up' their young behavior. Accomplishing toilet training brings with it some ambivalence - while it is a sign of growth and development, which is inviting to most children, it is also a sign of giving up some of the dependence that is inherent in being a small child. The latter is not so easy for some children. What does your son say about the situation? Does he indicate in any way that he is interested in accomplishing this task? What feedback do you receive from him?
A related discussion,
Toilet Training was started.
I have a four year old son that is not interested in pooping on the potty. I am not sure what to do.
in the same boat with my soon to be four year old. is the best way to deal with this is to just be loving and understanding of their unreadiness and have faith that they'll do it when they're ready or should we put some limitations on them in this area and not accept pooping in their pants, just like we wouldn't accept other bad behaviors.