Feral kids

Am I doing something wrong or is this just a kid/ age thing?
My son is so disobedient he won't listen, he talks back and damages things and does stuff he's told not to, he climbs on everything, can't seem to sit still, I can't take him out because he won't listen and he pulls things of shelves and with his sister they then both do it on their own they are not as bad but together it's impossible, at church they are feral so we just end up sitting in the kids room out back the whole time I know so bad behaviour is to be expected but this is driving me insane. So far nothing helps we try smacks, time out, sending him to his room etc and now he's starting to talk back or just plain laugh in our face
Son just turned 4 and daughter is 2.5

There both well behaved at daycare, things are busy but stable at home hubby and I happily married and don't fight .

There is no such thing as an easy age, just ages you find easier to manage. For me, age 3 to 7 is just not my cup of tea.

Advice would be consistency, get in hard and fast, do some time ins and natural consequences, and schedule in some one to one and family fun time.

Example, back chat results in me not wanting to talk to Liebs. He hates me ignoring him and so a reminder that I'll talk to him when he can respect me is enough. He struggles more with leaping around, so a trip to the park or some calming time in has a better effect.

Is it naughtiness to find boundaries or to get attention? I respond to the reason first and the action second.

DH responds to everything with time out, and that leads to a child who behaves to avoid punishment when his dad can see, and to Liebs not trusting his dad when he's worried about something. Also, if Liebs plays up for DH it is in a really major way. In for a penny and all that.

I'd say probably both I try give attention but sometimes that's not possible and I'm in the middle of something, I actually found 2 quite a nice age he was such a lovely boy even half of 3 was good but now it's like having a teenager last night he was just cranky and back chatting and I could tell it was because he was tired from daycare so I'm not as strict then