ok, so they have sn. As you may or may not know, my 2 both have autism.
We have had years of trashing stuff plus smearing of poo on walls, floor, bed and all over themselves. nice.
I can't tell you how to deal with it, I can only tell you how we deal with it.
We cleaned it up.
We realised early on that it was the way it was and we had 2 choices - wind ourselves up about it, or get on with it, and even laugh about it
Now don't get me wrong, we have our moments where we're tearing our hair out, but for the most part we have just accepted that the fact is - this is our reality and there's nothing we can do about that, and that made it so much easier to deal with. The kids weren't doing anything to us, in fact, they weren't thinking of us at all - it wasn't personal. So we cleaned it up, over and over and over ... and over and when we opened their bedroom door to find sweetcorn sliding down the walls, or see ds1 look up at us with a faceful of poo we cleaned it up. And then we moved on. Because if you let each incident stack on top of the last one, and the one before that, well, in the end you'll buckle under the weight.
We laughed - poo incidents (in or out of nappies!!) became "2319, 2319" (from Monsters Inc ) in a car and they start screaming? Scream along with them, or burst into a loud "The Sun Has Got His Hat On", or (if you don't mind risking a finger) wibble their lips while they yell. )
My kids practically grew up without crayons (grin) because we would get some, they would play and then sooner or later, they would decorate - and we would immediatly throw all crayons away. A couple of months later, process repeated - ending with crayons in the bin. They don't draw on the walls any more!!!
Threw toys and broke them? We went in with a bin liner. broken stuff in the bin. At times they had NOTHING left in their room!
We had plastic plates and cups for YEARS - they still use them a lot now, and they are 8 & 9, but tbh, I don't think they really need them.
I guess my point is (cos I realise this is turning into an essay!) that you deal with each thing on its own, each time as a single event, no one incident can overwhelm you. You find ways to laugh at it all. And you find a safe place (or person) to scream in/at when you really really need to. I suffer at times from depression, and I had TERRIBLE pnd with ds1, and mild with ds2 and when I'm low it's harder, but those times pass.
Every child is different, but when mine were toddlers, they didn't talk, they trashed everything, they were in nappies until 5/6, the 'professionals' said ds2 might never talk and didn't understand the concept of names , said they'd never have any independence, never go to mainstream, be in residential care as adults (my fault, i asked for their opinion based on their experience with other children as affected as mine!)...it was bleak - you should see them now! Calm (mostly!!!) and talking (after a fashion!) and just really great, sweet kids.
There's always hope. Things will not always be like this. Your kids are at the begining of their 'training'. It is a lot of work for you, but focus on them, on training them, and it will be less difficult. I promise it will be less overwhelming.