It's just not possible to recapture a read from 1969. I was not old enough to know or care about some of the science parts being really, really improbable...nay, impossible...as we had just been to the Moon and had recently landed a probe on Mars that put paid to even the dream of a Universe like the one Author Cameron created.
I loved revisiting Dave Topman and Chuck Masterson's flight to the impossible, tiny planet Basidium, all of 50,000 miles away. Their home-made rocket that traveled 25,000 miles an hour. Their bags od groceries to eat on the way there and back...two hours each way...two hours on Basidium, where they somehow spoke the language of the Mushroom People and solved a mystery that confounded the adult Mushroom People...the chicken that saved the day....
Nope, too old to get back there, but it was some good fun peeking back at the boyhood adventure that didn't have to make sense because what the hell actually does when you're eight or nine? It's starting to, but not quite yet does, blessedly.
I would give this to a six-year-old and read it with her. Maybe a slightly slow seven-year-old. No older than that, in today's world, and I'm not all the way sure it's even a good idea because gender roles and sex stereotyping are at the core of the story. So maybe, if like me you read it in your tinyhood, you'll smile and enjoy and keep out of reach of children.