Since you can't replace human breast milk at a store, I suggest buying formula with the earning from selling your kid's electronics. Or his allowance for a year. And then therapy before he does something else like pop the baby's water wings at the pool. This is clearly overkill. Just unplugging it for a few days is all he needed to do.

time to sell some toys

I hope you get that kid some help. thats really ****** up.

That's not average misbehaving. That's intentional destruction. At some point someone has given him permission to act that way. Good luck raising bail money.

This sounds more like jealousy caused by being neglected. It most likely isn't intentional but many parents inadvertently neglect the first born when they are bonding with the second child. Now when I say neglect, I don't mean failing to provide basic needs. I mean not providing the level of attention you think you're giving.

So, what are you going to do about it. I hope you came up with a good punishment. And then got him into counseling to deal with his feelings!

serious issues there, did your 10 year old realize that doing what they did would destroy the breast milk and risk their little sibling not getting enough food and consciously did it anyway?

ten years old is a bit old for temper tantrums. I personally would have tanned his hide for that, given him extra chores to do, and picked his favorite items and removed them from his room.

they're not too old for a spanking

Spare the rod....