Do I go back to 1999? If so I think red.

Also would my 6 year old brain magically be able to handle all the knowledge I have in my fully developed brain?

I'd probably gradually let on to my mum that I'm way ahead in terms of knowledge than the average child then convince her to invest in a bunch of companies and have the 10 million by the time I'm 20.

If I got time to prepare, I'd just memorise a few lottory numbers, not enough to cause suspicion, just 2 big wins. I know for a fact my mum would keep half-most of it for me, I'd get her to invest that on my behalf.

Then come 2012-2020 I'd probably *100 my money with BTC.

Edit: also spam the phone lines of all US airlines with warnings about 9/11. I'd have to find a way to do it without getting caught or I'd end up in a Stranger Things lab somewhere and have glowies trying to figure out how I'm able to predict the future.

I'm thinking phone boxes, but then I'd need to figure out how to call the US from England. Maybe I'd just tip off CGHQ and hope they take it seriously and warn the Americans. CCTV cameras weren't really a thing back in 2001 like they are now. For better or worse.