(rather solemnly)
Go back and tell my parents about the future, especially their own and that of the family.
If that ended up with me not being born, so be it. It would be worth the risk. Too much good could come out of it.
This assumes they believed I was their son, of course. Not likely. And, to be darkly humorous, especially not likely if I told them how the future *actually* goes, compared to how the future was expected to go, back in the 1930s.
'What's a microchip?'
'Well, a microchip is made out of silicon, and you run electricity through a million microscopic channels, and it deciphers them as 1s and 0s, and this is known as Digital. Everything goes by this language now, and with Digital you can perfectly reproduce music and video. They made punch cards into computers with Digital and something called the Central Processing Unit, and with computers you can ... well, see imaginary typing on a screen, sending messages anywhere in the world, take actions in Cyberspace - the 5th dimension, the dimension of the mind, but it's real enough place ... ask those arrested for crimes committed there - and have giant worldwide debates on just about every subject imaginable on Blogs and Messageboards set up on the Internet ... that's where they connected all the computers together with fiberoptics, worldwide, and ...'
'Can you start over with that? You said silicon? Microscopic channels? Like, through a microscope? And what do you mean by video ... television?'
'Well yeah, it's a little ... complicated. But then again, the modern home computer has far more power than the combined power of all the computers used to send the first man to the Moon, and ...'
'THEY DID WHAT?'
'Well, they also built jets to carry you around for about ... say, $20 in today' money, so you can fly from America to Asia or Australia in 18 hours, or Europe in 8 hours. Tens of millions do it each year. The jets fly at 600 miles per hour, at 7 miles high.'
'What's a jet?'
'Real fast air flow through super turbines. Special fuel dumped into the motor. Hey, want to hear about Pac Man? A favorite video game of mine.'
'Pac Man? An actor on TV, then?'
'Well ... uh ... I'll tell you later ... ever hear of freeways?'
'You mean ... ways of travelling better, faster, freely?'
'No, great big divided roads with limited access, full of giant trucks and millions of cars, crisscrossing all the continents except Antarctica, allowing you to drive anywhere. They gave up most trains, because everyone drives now, or flies, and everything is shipped on these freeways.'
'What about trolleys?'
'Huh? Oh, still have them in some places.'
(Heh. That's just the start. ENWorld forbids any discussion of politics, or ... well ... imagine discussing our current situation to the people of that time! A good thread for Circvs Maximvs, where it's allowed.)