While blue is the easy and tempting option, and I would live comfortably without needing to work ever again...
I would choose red. Considering I am approaching 40, and going by family history, I'll likely get cancer in my 50's or 60's... I think choosing red is a good solution to basically get extra 30+ years of life.
Also, with the forenowledge, there is a huge potential for life saving actions. While I don't think there is much I could do as a kid, it's worth a shot and I would have time to figure it out.
No amount of money can ever buy you more time. Only a six year old should take the blue pill. That's the moral of the story? I don't know, it's just a meme I guess.
Some countries don't have a robust foster system or a system at all. I would be rolling the die on homeless in the street in a dangerous place with dirt and flagstone roads.
Without knowing the conditions of recieving that offer, I wouldn't bank on being able to replicate it. You'd think whoever has the technology/magic to yeet your consciousness back in time into your 6 year old self without a time paradox would be smart enough to think of that infinite loop thing and avoid that.
But it would be an interesting way to achieve pseudo-immortality.
Or perhaps if the red pill is turn six today variant that pessimists think it might be, you might get actual immortality. Say we work out immortality in 2060, that might be difficult for someone 50 today, but easy to reach for someone 6 today.