Toothbrushing + toddler how-to, from Rachel:
My daughter is 2.5 and is able to regularly brush her teeth, but does not always want to. If I want to get in there to finish the job, I encourage her to open wide by singing "Ah!" like when the doctor looks down her throat. When a regular "Ah!" gets boring, we try doing high and low pitch. The gives me enough time to get in there. "Eee! " works for brushing the front of the teeth. When she is more cooperative, I talk her through doing the "Ah!"s and "Eee!"s and congratulate her for finishing by herself. Both sounds are fun to do in front of the mirror and can be followed up with spitting in the sink.
Related: How to get toddlers to spit out the toothpaste? Talk amongst yourselves.