Could Olivia have been Chris's mom?

Okay we all knon that Gordon has a sister name Ovlivi which Mile's aunt.
Plus Gordon has a nephew name Chris: Dose it mean Olivia is Chris's mom?

I thought about that too, but it's pretty unlikely since Olivia never married or had a kid and she was younger than Gordon, so she may have been a bit young to have a kid that age. What I'm assuming is that maybe Gordon has another brother or sister (most likely a brother since they have the same last name) that has never been introduced on the show.

I meant after she left Sesame street!

Hmmmm. I guess it's possible.

Here's something I found about Chris on Muppet Wiki:
http://muppet.wikia.com/wiki/Chris
(I had read somewhere that he had been Susan's nephew but I forgot where.)

Someone on YouTube (maybe it was sawing14 or wattamack4) made a joke saying that Olivia moved away from Sesame Street, got knocked up, and had Chris out of wedlock (hence he shares the Robinson name).

Oh brother. Like I said, I don't remember where I said I read he was Susan's nephew.
Anyway Chris has a fraternal twin (they had a show about twins. )And IRL Chris Knowings has a fraternal twin named Christy.

That's true!

Has it ever been officially said that Chris' last name is Robinson? Gordon and Susan's last name is rarely even mentioned on the show itself.

Yes. In the episode where he was introduced he called himself Chris Robinson, so he should be more closely related to Gordon than to Susan, unless Susan is related to another Robinson by sheer coincidence.