Following a day at the zoo and other fun attractions, Chuckie dreamt that he was an explorer going over a waterfall in a boat, which causes him to accidentally wet his bed. After Chazz determines that Chuckie may be regressing, he had Chuckie wear training pants, which is in between diapers and briefs. At night, the Rugrats try to encourage Chuckie not to fall asleep, so he won't forget to wake up to go to the bathroom. (thetvdb.com)