getting them in a car seat once they have gone rigid:
left hand firmly over hips/pelvis
right hand prepare straps for connection.
while left hand is still firmly over hips, use left hand fingers to tickle.
when child collapses in middle, keep held down with left hand and fasten straps with right hand. (last resort)
often, a knee placed between their legs (not on bits, of course, just like the lump of plastic they put on some highchairs) stops them sliding out the pushchair/carseat before straps are done. (again last resort when absolutely need to leave somewhere)
reins harness over the top of straps. special harness for car seat.
defusing a situation where you are both getting stressed: blow raspberries on them, or tickle them. makes both of you laugh and eases tension.
give the kid a choice. do you want to climb in the car seat or do you want me to put you in the car seat?
do you want mummy or dady to put your shoes on?
do you want the blue shoes or the wellies?
give them warning that you are going to do something else. choose a last go on something.
feed them before you leave. get that blood sugar back up and they become a bit more human again.
hugs. rock in one direction, both calming, especially after the park where they have been rushing round and moving in lots of directions.
develop rhino hide. standing contemplating shop shelves completely ignoring the hissing screaming biting child under an arm as if they are not there/ or walking out with such a child under an arm, or when older held across the body.
if you suspect autism, just quiet hugging, and rocking helps with no talking. They can not hear and are only working on feelings and emotions at that point anyway so words are lost.