Dad hack:
Remember, your younger kids want to do what your older kids do.
We used this to our advantage when our youngest recently didn't want to brush his teeth.
He'd clamp down on the brush, try to grab it from me, cry and be generally obstinate.
So to overcome it, we let him watch me brush is big brother's teeth
We made a big deal out of it
"Look how your brother does it, look how he's getting his teeth brushed, can YOU do that?"
Almost immediately our youngest pleasantly let me brush his teeth.
He wanted to be like his big brother. Easy fix and can be applied broadly.