Opinions please

As woman who been with partner like this eventually he'll start acting on words

Without knowing him it's hard to say how I would take this.
At face value, some people let their intrusive thoughts get passed their filter but a strange choice of words nonetheless.

What’s a fly kick?
I would assume like a fly (bug). So I would take it like a joke.

But maybe I just don’t know what he’s talking about so it seems silly to me.

I mean i tell my son I’m gonna put him in the bin ect (obviously joking) and realistically I don’t see how that’s any different from what your partner’s said, i think you’re just 2 very different people and realistically may not be as compatible as you originally thought x

It’s a little aggressive even though it’s a joke. Maybe wait to see if he does it again, because if it’s a regular thing and you don’t like it you can then mention that you don’t mind him having a joke but ask him to tone it down a bit?

Threatening physical violence is never okay imo and just not funny.

Are you Scottish ? 😅because this is soemthing that we just say to get someone’s attention if they aren’t listening. It also depends on the context. If he said it in a jokey way then fine but if he said it in a n angry, aggressive, annoyed way I’d be annoyed

The only thing that worries me more than this is .... when you guys break up his contact is then alone with your child

You need to be your child protector now

I don't believe that its as deep as leaving him, but I do think you guys need to have a talk just about how to have boundaries when it comes to children. You guys are both learning how to be parents, so there should be some grace there. Just vocalize your expectations and see what he says and does. If he cannot compromise, then you may want to rethink your relationship.