Pour milk into the blender and add the dates. Blend until the dates are dissolved into the milk. This took less than 30 seconds for mine. The goal is to have a sweetened base for the smoothie, without chunks of dates. (The first time we made these, I tossed everything in all together and the little bits of dates were pretty tasty that way too!)
Add the banana and berries. Puree until the smoothie is thick and smooth. This smoothie turned out pretty thick. I scooped half of it into a bowl with a lid and froze it for a couple hours. My kids enjoyed it as ice cream later in the day. Enjoy!