Would you cut off someone that lied about having a child?

What your colleagues do in their private lives is kind of irrelevant. You still have to be able to work with her. Stay out of it.

I think that could be a possibility

Its a hard one unless you know the reason. Could it have been a child that died years ago. Is it person who had desperately wanted a child and couldn't. Is it a silly comment that shot out her mouth when she first started trying to fit into a conversation and had to carry it on.

How do you know?

Does she have a stepchild? Estranged child? Adopted child? Deceased child?

If there is no explanation and it's a completely made up lie, then yes it's very odd and I would keep my distance personally.

Honestly it's a red flag for me. I get that we all lie a bit to smooth things over but something as big as that is concerning. I wouldn't shun but I'd be a bit wary of them. Fine for a casual friendship with a colleague but I wouldn't enter a relationship with someone like that for example.

I honestly would suspect she’s suffered a bereavement of some sort (possibly a stillbirth) and has not dealt with it and it’s caused this sort of behaviour. I’d be wary but not cut her off.

How was she found out? Are you able to probe gently at all?

The OP said that wasn’t the case. I have no interest in why. I just steer clear of liars. In a workplace that’s easily done. I can be polite and still steer well clear.

Her personal life is none of your business. Leave her alone. There was a reason for the lie and you dont need to know why or understand it.

I knew of someone who every year said she was go3ung to her son's for Christmas. When she died it was discovered she had no children. We concluded she didnt want people feeling sorry her being alone and taking pity on her.

It seems like a pretty sad lie. I would probably take her as I find her. I'm sure the reason for the lie will become more apparent in time.

Honestly, OP, I would reserve judgement. You have no idea what went on on her life years ago. Maybe she gave up a child for adoption. Maybe she had miscarriages. Maybe she was coerced into having an abortion. Maybe she did have a child who died. In any of these circs, referring to her adult child to a stranger lets her remember her child.

It's also possible that she lost access to a child and doesn't want to tell people that, so you are unaware that she does in fact have one.

Or, it could be that people really judge childless women and she doesn't want that judgement at work.

If she's a friend, you could say "Oh, I didn't know you had a child!" when you overhear her saying it, and see what she says.

I read a post about a woman lying that she had a child because she was sick of coworkers who were parents getting days off/early finishes/being allowed to take time out for strike days etc. She was fed up and made up a child, so when she got older, she presumably had to keep up the lie.
More seriously, sometimes if someone has lost a child to miscarriage or stillbirth, they still consider themselves a parent. While I would never tell a lie that the child I lost was "on holiday last week" or act as if they're still on earth, I do sometimes hesitate when asked how many children I have. No one wants to say to a coworker or virtual stranger in response to the usual query about your fecundity, "Hey, I have a son and a daughter, and another who died", but equally, saying you only have 2 seems like ignoring the stillbirth as if they don't matter.
So I would say it would be awful to treat her badly or cut her off.

Wouldn’t you find out in this case why she lied before giving a wide berth? What if she did have a child and no longer does?

How did you find out she doesn’t have an adult child OP? Do you know she definitely doesn’t have one?

If she’s just your colleague, it’s not your business or worry how many children she has or not. 🤷‍♀️

How do you know there is no child? Maybe she had the child adopted? Or a mental health condition etc ?

How did you find out she was lying?

If it hadn't affected me in any way (she hadn't been asking me to do something for her so she could see the fictitious kid or something), I'd tell myself she wasn't having mental health issues (or a dead child, or a child that was taken from her) AT me, and let it go.

Why? I couldn’t give a damn why anyone chooses to lie. Why should I have curiosity about it? If someone lies I give them a wide berth in future. Liars are dangerous.

Same - my brain wouldn't instantly go to 'cut off'. There are so many permutations here. Some might be very sad and difficult. Some may not of course. But face value judgements are rarely solid ones.

Why would your first port of call be anything but trying to understand?

It's clearly an odd thing to say, there must be something behind it.

Depends on the circumstances and why she did it.

If it was someone inventing a whole load of details and backstory about a child and giving them a name and constantly talking about them, I'd think that person was probably deeply unwell and while I wouldn't 'cut them off' I would certainly be maintaining a safe distance and having a little chat with them about why they lied and suggesting that they got some mental health support.

If it was someone trying to come up with an excuse for needing time off and they said 'It's my son's birthday' or something, and then people said 'Oh, didn't know you had a son, what's his name, where does he live' etc and they just panicked and answered the questions, and the whole thing spiralled and they had no clue how to extricate themselves from the subterfuge because how can you suddenly say 'Oh yeah, that son I mentioned? I made him up to get a day off' then I'd find that fully hilarious and would absolutely want to be friends with them.

I would avoid her

Depends. I worked somewhere that gave preferential treatment to parents, first dibs on annual leave, they were the only ones allowed time off at Christmas and in August, and they were always allowed to leave promptly at the end of shift- whereas the rest of us would have to stay until the work was done. I would have happily started to drip-feeding in some imaginary kids if I had planned on staying there long-term.

In the case of your colleague do you know why she has done this? If its for practical reasons to avoid having to work certain holidays etc., that's one thing, but if its not for that reason, its an odd thing to do that I would imagine comes from quite an unhappy place. If this has recently been 'discovered' then she may feel really humiliated by it.

I agree with what Kelsey Graham said, ' To judge someone without first hearing their story is one of the greatest evils.'