This may not be your situation but worth a check on.
My Gran daughter did this and had a pacifer to boot. Horror to me but parents would not listen. Easier to pop on in then hold and cuddle children for one now a days to sixties.
Anyway She ended up having several teeth filled and pulled and m issing up to five years old.
To now five years later braces where she had to have something winded up in them every day for a long time.
And now braces and more surgery.
Something about the jaw.
Any way if they would of avoided the pacifer and had her jaw and bones checked this would of not happened.
Oh no bottle in bed also would of helped.
Anyway her bones and teeth was broken,over grown etc.
So please see if a medical reason is why.
Doctors refused to send her to a dentail bone specialist and now she has to live with all this and braces, expectly for a girl is hard to be in fourth grade.
Hopefully your situation is just a away for the child to get attention.
Attention,nervous,unknown grinding is mild reasons.
Above is the example of a problem not being addressed.
So thank for being a concerned Mom.
Knox flavor jello mixed to directions,
Cheerios not generic or cheap brand on a string ...tie strongly.
Soak cheerios a moment with quick dunk or so in jello.
Freeze or chill.
Later when hard and set this will be a good treat for the child if the doctor oks it.
Teether to be used with adult watching.
Or you can place cheerios minus string on their high chair tray.
And if doctor ok the rest of the jello is a good treat for Mom,other children and baby.
Toss out the rubbery top .
hope this helps.
Also to prevent damage dentists and doctors can place a sealer over the teeth or for older children a guard they told us or a spacer(it helps even the teeth and it may hurt not at all but makes it uncomfortable to do this so this unconsious grinding stops soon.