My brother, who is 355 days younger than me, was very ill when he was young. He had severe asthma & excema (had to be wet-wrapped & creamed all over every night), had callipers on both of his legs due to Perthes disease, was behind in school as he was always in the hospital and was very small for his age.
I was healthy and average size, therefore always bigger/faster etc. than my brother.
When I was about 8 and my brother was about 7 I caught this lad in my brother's class (so one year younger than me) who had cornered my brother behind the school bins & was whipping him with tree branches & saying horrible things to him. 
I punched him in the face, bloodying his nose, & my best & I friend put him in the big bin.
His mother got called in, took him to the doctors' about his face (his nose was quite badly damaged) & we got in big trouble about bullying younger children. We were never cruel to younger children, this was a one-off offence but as it was 'serious' we were in big trouble.
Anyway, when I left primary I didn't see this chap again for a very very long time until last week when I went out with some of DH's friends & he was a friend of DH's friend and was there. He is huge now! I didn't recognise him but he told me who he was. He was very pleasant and we got on OK but then he said "Do you remember that time that you and ... ganged up on me & broke my nose?" Attempting to make me feel guilty.
Am I unreasonable to still, now that I am older and wiser, not feel guilty?
I suppose I would tell children now to tell a teacher & not use violence, but I can still picture my poor little brother being so upset - he was regularly bullied by this boy and I think he deserved the beating.