Originally Posted by Often1

OP says that he has Pre-Check. This means a standard scanner (magnetometer in the olden days). No need to stop, raise hands and all of that. One just walks through the scanner at normal speed.

No need to alert TSA in advance or to even say anything at the podium as that simply drags out what is a simple process.

On the extraordinarily remote chance that there is an issue which causes OP and family to be referred to another line which lacks a "mag," that may be the time to raise the autism issue. But, to be clear, this is a remote possibility and there is no need to raise this in advance.

99.9% of the time, any child accompanying a Pre-Check parent (or who has Pre-Check himself) will walk through a standard mag at normal speed and there will be no issue whatsoever. This will be faster, less intrusive, and easier overall than anything else.