I want to return to Italy

https://www.gov.uk/return-home-voluntarily

You can apply for help to return to your home country. This is known as ‘voluntary return’.

You can still get help if you’re already making your own plans to return to your home country.

They'll answer all your questions properly and help you avoid any legal issues

Thanks Fred. I don't want voluntary return assistant, I  can pay for my return ticket .
I want to know if I can just buy my ticket and leave without having problems?

I am not returning to my home country.  I want to return to Italy where I have my permanent resident permit

Joy.ob wrote:

I am not returning to my home country.  I want to return to Italy where I have my permanent resident permit

So talk to them and see if it's possible without action being taken against you for the overstay.
There's a better than average chance they'll want you out of the country so, as long as immigration offences are your only crime, they'll probably sort out your problem quickly and easily.
Just turning up at an airport might be fine, but this way will look after the lot in one and remove any worries you have.
If you've been working illegally and try to take cash out of the UK, that might well lead to problems.

Thanks Fred.
I will buy my one way ticket and try

Joy.ob wrote:

Hi everyone. I am new here.
I living in UK with my four years old son illegally and we have Italian permanent resident permit and I want to return to Italy, can I buy our flight ticket and leave?

Do Italian permanent resident permit holers lose their permanent residency by being absent from the country for a certain period of time?

No because I haven't stayed out of Italy for more than a year

I haven't stay outside Italy for more than a year

@post

There is no 'double residency' allowed in Italy. You will lose your permanent resident status if you are out of the country for 2 years.