We are thinking of moving to the Denver area due to my husbands work in Golden. Our children are 7 and 1. What are the schools like in this area and are there any other British families with children around the age. Many thanks

Denver is a large area so I hazard a guess you'd need to be more specific.

City-Data.com - Stats about all US cities - real estate, relocation info, crime, house prices, cost of living, races, home value estimator, recent sales, income, photos, schools, maps, weather, neighborhoods, and more may provide some idea.

You need to look for the best high schools. The best high schools tend to have the best feeder schools and and are in nice areas.
You start with the US New High school rankings. I find this ranking to be the best indicator and it covers the whole lot. It is what most relocation advisors will use.
https://www.usnews.com/education/best-high-schools

You can search for private, magnet, charter and normal High Schools.

Once you've got your couple of high schools, go to the school district website and find the feeder schools. Then google those schools..... citydata is good for most things but my reservations are that 1. everyone thinks their school is the best and 2 the folks end up going off on a tangent in the discussion...

That's a useful national starting point. But ultimately, you need more detailed local data.

Also, think about what constitutes "best" for you and your child. Some high schools with the highest academic performance can represent a miserable environment for a child with average abilities. The competition can be crushing.

Gaining college entry can be a lot easier if you're in the top 25% of an average high school and way harder if you're in the bottom 25% of a school with amazing academic performance.

I have two very smart kids (top 2% nationally) who struggled quite a bit at a nationally ranked high school. In that setting, they were just average.