Hello Dr, my problem is concerning my child of 8 yers & half old, he

Hello Dr, my problem is concerning my child of 8 yers & half old, he is very difficult , agressif in his plays with sister & brothers and also in his Classroom. FYI he is good in his school but he is lying a lo, a last thing he did is :that i gave him a money to buy a books from the school , he want and bought cookies & Limonad to his colleagues, this did it twice in this week. i tried to discuss with him and tell me the truth but he didn’t. to help you we are 5 at home father, mother & 3kids and we are happy, we are not facing any problem which can disturb him, now i’m stucked i do’t know which solution i follow with him, could you help me before i lose him. Thanks Dr