Kids aren't dumb, they just lack refined thinking models adults develop as they grow up. Eg: I think we all have experienced reading again something we read young and loved and finding a lot more meaning in it.
(I'd still avoid showing some things to them of course.)
At first, it's about a robot and another robot doing stuff. Then they're on a journey. Then the desire for friendship. And hospital. Then (gradually) the idea of different motivations comes in. Perhaps some ecology. Then conflict, etc.
All the while, my daughter is delightfully more interested in robots and space travel than standard 'pink princess' fare.
Of course, YMMV.
My favourite example of this comes from comics:
Try looking at Alan Moore's Swamp Thing run (issue #20 or 21 of volume 2 - the 1982 revival). It's a masterpiece that is well worth reading as an adult.
Now try looking at early 80's X-Men. While e.g. Days of Future Past is good, one of the reasons some of the arcs like Days of Future Past stands out so much is that many of these series were so full of excessive amounts of tedious exposition recapping things that just happened and reminding about and explaining things to the reader all the time, and the standouts were the few exceptions that treated the reader as a person with somewhat more mental capacity than a goldfish.
At the time, I didn't see the difference. I enjoyed X-Men and Swamp Thing equally. Now, going back and looking at those old X-Men issues is - with a few exceptions - almost painful and only worth it for the nostalgia.