In Avengers: Endgame, during the scene where Tony and Steve lose the Tesseract to Loki and now they improvise and travel back to 1970, Tony accidentally meets Howard and they start some small-talk in the lift.
During which they say to each other:
Tony: I have a girl.
Howard: A girl would be good.
Throughout this exchange we see that Howard is quite nervous about being a father.
When Steve Rogers (Captain America) gathers the extra Pym particles and signals to Tony that it's time to go, the following conversation occurs:
Howard: Smart guy (talking about Tony's dad)
Tony: He did his best
Howard: The kid’s gonna be here and there's nothing I wouldn't do for him.
So did Howard know he's having a boy?