Just give him some time...sometimes children develop this kinds of fear related to passing stools..make it is a pleasant experience for him by rewarding him stars or smileys etc..or by praising him..dnt discuss too much bout it infront of him
Next Steps
observe the time when he passes stools daily and try to take him to washroom playfully
Health Tips
the more you drag this the more difficult it vl b..ignoring the problem and supporting him is d best thing you can do now..