ASD moms: S/O obsessions

How often do you find that your child's obsession's change?  For the LONGEST time, he loves spinning things, especially wheels and ceiling fans. Still does but not with as much passion. Recently, he has discovered the toliet and must flush it often, I think to stim on the spinning water.That has come in handy with potty training ). He has no fear of the potty. Also recently, he is obsessed with a/c heating vents. He loves taking the vent covers off ours at home and peering down them. Also, he loves to throw things down the vents (note to self: get them cleaned out before we turn on the heat) When we are in stores, he has to spot every single vent and point them out to me.

Is obsessions/passions something that always evolving to something new?  Since he stims on spinning objects, is it something that he will always enjoy or find comfort in?

The other post had me wondering. )