This paper presents a novel platform for expressive music making called Hitmachine. Hitmachine lets you build and play your own musical instruments from Legos and sensors and is aimed towards empowering everyone to engage in rich music making despite of prior musical experience. The paper presents findings from a 4-day workshop where more that 150 children from ages 3-13 built and played their own musical instruments. The children used different sensors for playing and performed with their instruments on stage. The findings show how age influenced the children's musical understanding and expressivity, and gives insight into important aspects to consider when designing for expressive music for novices.