Katie,
Its hard to get them to brush hey! We always brush our teeth together so Ds will copy! I try to give them a good brush, then let him play with it just so get used to the feeling.
We dont rinse after brushing its too hard. How much paste do you use? They only need a 1/4 of a pea size on there so its not that much for them to swallow!
HTH good luck! xx