My ds1 (3 yrs) has started pushing around his little brother (18 mths) and looks like he thinks its funny. He doesn't seem to be able to leave him alone. I try not to be a yeller, and attempt to explain to him that it is not a nice thing to do, it hurts his brother and makes him feel sad. I have asked how he would feel if a friend pushed him and he says "sad", but I presume that at this age he can't extend this to empathy for his brother. I guess its fairly standard behaviour for siblings this age, but it is just constant at the moment, you can tell him "no" one minute, and he will be pushing again the next. It's quite hard to bear to see your baby son in tears all the time.