Somebody mentioned that I may be able to get extra pension or child benefit when I get to the
right age. I wonder if that will be frozen if I live in China.

If you are from UK - then I think that when you reach the age to claim your pension and you have permanently left the UK then the pension is frozen as of the date you left.
https://www.gov.uk/state-pension-if-you-retire-abroad/rates-of-state-pension

Here is a link to check your UK State Pension https://www.tax.service.gov.uk/check-your-state-pension

Of course if you aren't a UK citizen then it obviously doesn't apply...