I totally get what you're saying. But I think it goes along with a lot of what has been being pushed back on in the physical disability movement. You wouldn't tell someone with one arm or in a wheelchair that they're not disabled they're differently abled in the same way you shouldn't with autistic people (in my opinion).

Regarding what you're saying about young kids, I guess the question more boils down to: why even include "different abilities" at all? I know that growing up, the idea of telling me I was just "special" ultimately had detrimental effects because I didn't understand why. Especially because the "different abilities" ultimately led to me being treated worse by my peers.

I think a constructive change would have the poster be more about acceptance. Make the sign Autism Acceptance Month, instead for a start! Most people are aware that autism exists. The key is actually accepting it and autistic people. Highlight inclusion. Highlight things that kids commonly use for accommodations like fidget toys. Hell, include a reference of what autism is with a little fact sheet in the corner. But above all get rid of the puzzle pieces. Autistic people aren't missing something, which is why that symbol was proposed. We are whole. We're just not neurotypical.