I'd firmly indicate that unless it intended to use its power to take over my action, I'm not a puppet for it to enact its sick fantasies. Several expletives would be involved. Then I'd go about my business.

I will tell him, "A benevelant god would not ask such a deed. He/she would never have created a situation in which such a deed be necessary." Then, I'd kindly bid him goodbye by saying, "Go fuck yourself, you sadistic bastard."

Get the fuck out of my face. You are an illusion.

Not sure anyone could say with certainty what they would do given the line you added, "you are convinced this is God"

My initial reaction is to reject the thought experiment as it's founded on a faulty premise, but to entertain the question there would be a series of questions necessary:

Why should I sacrifice my child?
What is the reward or punishment for compliance or non-compliance?
What is the proof that you are God?
Is my child my real life child, or am I Hitler's dad?

just to name a few...

Anything appearing to me telling me sacrifice my child I would say no, be it "god" or someone with a gun to my head - the answer is no

Get really fucking high and wait it out a bit to se if he fucked off again!

Isn't that schizophrenia?

Straight to a&e and ask for medication

Assume I'd had a psychotic break and baker act myself.

I'd tell him to fuck off.

Fuck you I don't need your crap.