Heat the oven to 350° and line a 12-cup muffin tin with bake cups. In a large mixing bowl, use an electric mixer to cream the butter and the sugar. Beat in the eggs, then the milk and vanilla extract.
Sift the flour, baking powder, and salt into a medium-size mixing bowl. Pour the dry ingredients over the wet ingredients and stir well, being careful not to overmix the batter. Use a spatula to fold in the berries. Spoon the batter into the muffin tin, filling each cup about three-quarters full.
To make the crumb topping, stir together the sugar, flour, and cinnamon in a small mixing bowl. Using your fingers, work the butter into the dry ingredients until the mixture is crumbly. Your child can then sprinkle the topping over each muffin.
Bake for 20 to 25 minutes or until they are lightly brown and a knife inserted in the middle of one comes out clean. Cool in the tin for 15 to 30 minutes before serving--if you can wait.