Would you deem this appropriate for ex to be saying this

[Hobbitjar]

A question on ex telling my young child stuff, don’t tell mummy but I’m moving away? Don’t tell mummy but I’m getting married? Don’t tell mummy but I’ve had arugument with gf so not she isn’t moving with me although they only been together less than 4-5 months at most so now child is upset she will not see his gf child anymore.

Isn’t too much to tell a child not to say anything. Then my child tell me anyway and said but I will tell you even though he says not to say anything. 🙄

Tbh I’ve told my kids to not tell their dad anything about me, not so much as to say something then say don’t tell your dad but I have told them not to tell him anything about my life

Weird; if he didn't say anything, she probably wouldn't even think of telling you, would she? Sounds like he actually wants you to know!
In any case yes, of course it's stupid. But your child sounds very sensible by ignoring him.

I watched my poor niece grow up between two constantly bickering split-up parents and she learnt from a very young age to keep two separate lives and be a pathological liar! Her ability to lie at the age of 6 was outstanding. We were very worried about how she would be as a grown up but I have to say she has turned out amazing - although she is a very carefully spoken woman as she thinks very carefully before she speaks. I guess a skill she developed as a child as she learnt to avoid accidentally spilling secrets to the other parent.
I don't have the answer because it must be incredibly hard - but I do see red flags asking a small child to lie and keep secrets as this sets them up thinking its OK for them to lie and have their own secrets too.

I guess I would tell DC that you don't keep secrets only surprises - like gifts. When your DC tells you things I would not make a big thing but sympathise/support their feelings.

Absolutely don't ask them to keep secrets.

I would try and have an off the cuff chat with Ex that DC is upset at being asked to keep things from you so don't tell them anything you don't want me to know??? Depends on how well you get on? Send some links as to why it's a damaging thing to ask?

I would mention to the ex that 'don't tell mummy' isn't working and very foolish and confusing to your dc to know about events that haven't happened and by the sound of it unlikely going to happen.
Unfortunately your dc will learn not to trust what his father says.