Please help-toddler discipline

[Singbluesilver]

My beautiful wonderful nearly 3 year old ds1 has become really hard work recently. He hits our 3 month old dd, constantly does the opposite of what we ask and I have no idea what to do.
My dh wants to smack him, I have said absolutely not. This will not happen. We have tried time out/ step/ explaining why we are unhappy with his behaviour, but nothing works. I am beginning to feel a failure, plus I'm so tired with new baby and toddler. Any advice on how to gently discipline would be much appreciated .

Time out etc. never worked with my DS1 either. What we found to work was removal of whatever toy he was playing with/in love with at the time - after a warning. Or turning off whatever he was watching on TV.

Still works now at nearly 4.

I've heard that it takes a few months for a child to realise that a new baby is here to stay and that's when they regress because of it. My DS was awful to my DD when she was 3 months-ish but he wasn't 2 yet (he's now 3.5). Time out and until has never worked with him and praise only started to work when his sister was old enough to get it. Two things that have worked for us are: understanding what's behind his behaviour and explaining it back to him, along with reward and punishment with warnings and explanations. Nothing like smacking, ' more: I've already asked you not to hit your sister, explained why and told you what would happen if you did it again. You did it again so now I'm taking away your Lego'. Or whatever.

To add -if you ever threaten to do something absolutely go through with it or else they will never take it seriously. If you threaten to go home if they misbehave then do so, no chances after the warning. It can be an awful inconvenience at the time but earns you so much happiness (you and child) in the future. Same with rewards.

Thank you for your replies and advice. I do think we need to change the way we do things. Today he is an angelic little ray of sunshine!