My youngest is 11, 12 in a few months. My other DCs are adults. When he was about 18 months, he had bronchitis and was admitted to hospital for about 3-4 days.
As a toddler, he was very aggressive, we didn't really give him consequences, we just told him ‘no’. When he started school, he was the same, he'd hit other children for no reason. We did give him consequences for that though, like no treats etc. He was suspected to have ADHD by school but it was ruled out. He did start behaving at school, although he'd still hit other children and when asked why he used to say it was ‘funny’. He also was excluded once.
He's still very violent at home, he's also started telling us to fuck off and to ‘die’ whenever we try to discipline him. He finished primary school yesterday, and he already started being violent towards us. I just feel like a bad mum, none of my older DCs were like this, they were kind to everyone and would never hit anyone!