They shouldn't be saying that, get the person on their own and tell them what they're saying is wrong and if they carry on then you'll report to the headteacher. If the problem persists, involve the head.

tell them to stop you are still the authority if it continues tell everyones parents

I would maybe talk to some older teacher friends to see if they know what to do....

But, maybe you should embarass him in a way so he never does it again...

I really don't think you should ignor the situation and hope it goes away....I don't know. I wish I did know.... I always freeze up when I've been in uncomfortable situations like that before.

Edit: if you do descide to try to talk to the child alone - take another adult/teacher with you...cuz I wouldn't trust that kid at all from trying to reverse the situation.

Don't worry about embarrassing them because their remarks are obviously causing discomfort for you. If they can say these things audibly, then they are asking to be publicly held accountable for their conduct. Tell the boy(s) that what they're saying is inappropriate and you won't be spoken to that way. If they continue, consider taking away privileges, such as making them clean the classroom during recess. Keep an incident log in case anyone questions you, detailing what happened, who did it, and how you handled it. Report their behavior the headmaster and send them to his/her office as needed. Let the regular classroom teacher know so she can be aware of what's going on while she's away; I'm sure she'd want to be kept in the know. The kids are awfully young to be this brazen.

They are embarassing you, so say what you want to say as long as it is appropriate and if it embarasses him, maybe he will stop. I teach first grade and I know you have to be careful, but they should not be allowed to treat you that way either.

When I was a student/substitute teacher, I got similar comments. I would use humour to offset the comments. Are you married? No, is that an offer? Do you have a boyfriend? No, but again, is that an offer? He likes you. Really? Don't you all? He thinks you're hot. Well, he's got good taste. If you can "burn" the kid making the comments, the comments usually stop because now the other kids are laughing at him instead of picking on the other kid or you.

tell them that those remarks are inappropriate at school
this is sexual harassment which is against the law, esp in schools
take the offending students into a private conference and have the principal and/or counselor with you
start off by telling them that the remarks are inappropriate and sexual harassment and that you do not like those comments then let the principal or counselor take over
they are doing it because they can and they must be stopped now
forget about embarrassing a child...they are embarrassing you and making idiots of themselves and if the behavior is not addressed then they will think that it is ok to continue the remarks.
they may not know better now but they should soon
remarks such as those may be appropriate at home or in their neighborhood but under no circumstances are those remarks appropriate at school
we just don't talk like that at school