I have a child with an IQ over 142…
142+ is very, very high. Although I see hundreds of gifted children every year in Australia, Singapore, and other places, I probably only see a single 142+ every month.
142+ today is about the equivalent of 160 back in 1980, and 180 back in the 1920s (thanks to increasing IQ via the Flynn effect).
Please read these two books written specifically about children like yours:
Hollingworth’s longitudinal study on gifted children about American IQ180+ in 1920 (free book):
https://dl.bookfunnel.com/vq2rk78y6y
Exceptionally gifted children, a book by Prof Miraca Gross about Australian IQ160+ in 1989:
https://www.amazon.com.au/Exceptionally-Gifted-Children-Miraca-Gross/dp/0415314917
(There are two versions: the 1993 first edition, and the 2003 second edition. Both are okay. Should be $10-40, check eBay, Fishpond, etc.)
Related article: https://files.eric.ed.gov/fulltext/EJ746290.pdf