There is much wisdom in the replies here, but I just want to add on to one point that how you handle whining in a neuro typical kid is probably not how you would handle it in a kid with SPD. It could be very harmful.
I used to refer to the book The out of Sync Child. I’m not sure if that’s still recommended as a resource or if there is anything better out there these days.
Another thing I would say is that most parents of kids like this later regret not having been more gentle. It’s often hard to figure out where to draw the line with behavior and that’s why research, a specialist, or a diagnosing can be helpful. Maybe start with a referral from the pediatrician to an occupational therapist who works with kids with spd.
I have two kids with SPD. I used to hear it morphs into anxiety as kids become adults Maybe. I’m not sure. But it still stays as part of their neurological make up and will show up in different ways. It’s better to be aware if that as these kid mature because it can help give insights into behavior later on.