I would love to hear more about your experiences running a maths circle here in the UK. My two daughters are a little young (3.5 and 0.5), but this article has inspired me to get the ball rolling.
The NRICH material is really good: https://nrich.maths.org/teachers/early-years
There's some NRICH funded research that showed that exposure to symmetry and reasoning at this level was much more predictive of future abilities than numbers and counting. I think when parents try and help at the early stages, they often try to e.g. get their kids to count to 100, which is conceptually identical to counting to 10.
For number fluency there is the free White Rose '1 minute maths' app, which does a very nice job of gamifying subitising & etc. A lot of primary schools in London seem to have adopted the White Rose teaching resources. https://whiteroseeducation.com/1-minute-maths