How to stop things escalating with my kids?

[ICantStopEatingg1]

This morning for example my 5 year old was showing my eldest (9) and me a trick he learnt in school. The eldest kept shutting him down with “that’s so stupid”, “that’s not a trick”. I encouraged my 5 year old to continue showing me. It escalated by the 9 year old kicking the 5 year old. I’m really upset as this is a daily occurrence. My 5 year old son is very gentle and sweet whereas the eldest has always been like this even as an only child so there’s no jealously. I don’t know how to stop things escalating.

I told the eldest off and really shouted at him which has made me feel really upset and guilty. I over compensated by being nice to the 9 year old. I feel like crap right now. Can someone please help me by telling me what I should have done? I did before shouting tell eldest there will be no iPad today as a consequence. Eldest when calm I tried to discuss but was told the youngest was being mean by showing a trick he didn’t want to see! It’s always someone else fault!

Shouting and then overcompensating is giving a really confusing message to the kid. If he didn't want to see the trick, it is fine. Perhaps, you could have discussed more positive ways to say "no" i.e. "Bro, I don't want to see the trick. Show it to mum and I will go up to my room to do some drawing".
Sounds like your 9y/o has difficulties regulating his emotions. It may be worth looking at this specifically rather than assuming that he is just mean to his brother out of spite. Some positive strategies like assertive (not aggressive!) communication, taking time out when feeling overwhelmed, box breathing, sensory toys/activities...

ETA: Try spotting the trouble earlier. For example, after the very first negative comment, you could encourage him to step out of the room or switch his attention to a different activity. The fact that you encouraged your 5y/o to continue without addressing the feelings of your 9y/o could have signaled that you don't value his opinion. And fair enough, if the opinion is not agreeable but acknowledge it without validating by reassuring him that he doesn't need to watch the trick and why not do something else instead while you watch the rest of the "show".
According to PBS, every negative behaviour is due to unmet need. So some detective work about what the unmet need is may be helpful.

@Catza thank you. I will try this

Admittedly mine are younger than yours, but I have had to speak to my 6 year old about how we have to encourage little kids when they are learning to do something. That it might not be that impressive to us, or they might get it a bit wrong, but it's nice to tell them they did a good job or whatever.

Failing that I'd just say if you aren't interested then go and do something else and stop winding up your brother, or ask the big one to show the little one how he does a trick.

This probably very much depends on personality. My eldest would definitely get shouted at for kicking his little brother or vice versa, so don't feel bad about that.

Nip it in the bud much quicker in future. “Your little brother is showing me something, if you don’t want to watch you can leave the room or look away”. If he interrupts or interferes insist he leaves.

You can try having a little chat at a different time when it’s just you and your older one together, explain to him about being kind and encouraging to his little brother.

Telling him off then being nice because you feel ‘guilty’?

Children dream of eating endless sweets and staying up all night but subconsciously they need and want to feel that a grown up is fully in control and in charge. That’s why they regularly kick and test the boundary - to feel psychologically safe.

If they don’t feel you’re ‘in charge’ they will escalate bad behaviour because they’re provoking you into caring. And eventually, if it’s left to continue into their teens, that rots down into a complete lack of respect for you which is sometimes irretrievable.

Parenting involves putting in boundaries and lovingly and boringly upholding them. He kicked his brother for no reason which rightfully gained a bollocking. Your feeling guilt that it shouldn’t lets everybody down.

I would have stopped everything for a minute and told the 9 year old they didn't have to watch and were free to leave and go and do something else.

My 10 year old can be controlling like this but I repeatedly talk to him about things he can control and things he can't. In that situation he can't control his brother showing mum a trick but he can control his own body and walk away if he didn't want to watch. Any mean ness or hitting is absolutely unacceptable and losing the iPad more than fair. Stick to your guns. You're their mum not their friend.

You need to act faster and earlier. Would you have been able to physically intervene and stop the 9 year old kicking his brother? The younger child needs to see you do that.
Does the older child resent the younger one getting your undivided attention? They both need time with you to themselves, I know that can be hard.

Mixed messages for your 9 year old there. What he probably needs is more positive input and understanding of the effects of his behaviour on others. Calling people stupid is damaging, yes they are siblings (rivalry) but i think working on the relationship between them would have a positive impact. It's hard enough getting through life without having your own family members being hostile towards you. I think your 9 year old can understand this, but bring it from a place of 'let's sort this out and make the house a better place for all' rather than 'your behaviour is awful' - he will respond much better to positive parenting here.