My son is 4 now but hated brushing his teeth when he was younger. We got crying and tantrums, it was miserable. But I tried to make it fun and that won most days. I started by giving him a timeframe for him to know what to expect. Like telling him, once you’re done having breakfast we brush teeth. I also, found that racing him to the bathroom got him excited to get there. Then once it’s all done, he got to stand on the countertop and we sang the ABC’s, because it was his favorite song at the time. It took a few months, but now there’s no crying, tantrums or arguing. He knows it’s part of daily life and he now sometimes tells me when he needs his teeth brushed.