I have a 4 year old and a 19 month old. According to our pediatric dentist, the parents still need to be brushing their teeth at this point. They can have a turn after mom or dad has brushed.
He showed us how to hold the little ones in order to brush their teeth. If you're right handed, lay your little one down cradling him in your left arm with his right arm tucked against your side and your left hand holding his left hand/arm to keep it out of the way. You can then lean them back and brush. They will probably fuss at first but you can gently wiggle the tooth brush in their back teeth and twist it gently to open their jaw to brush. No, it's not easy at first.
We sing songs or joke about cleaining off all the food they've eaten recently..."Let's clean off the yogurt, and apple, and cucumber, and, oh! look there's some cereal to. I'll get it!" If they sit still, they get to brush when we're done; if not, they get to try again next time.
My 19 month old has gotten used to sitting on the cupboard next to the sink and my older son stands in front of her and demonstrates how to open his mouth wide and say AH so I can brush her teeth. She likes copying him.
Our dentist is:
Dr. Matt Karsten
Kids First Pediatric Dentistry
Elgin, IL
847-717-KIDS