I think like devnonymous says, SnapCircuits are a good choice. They aren't breakable and can be quite fun to play with. But, to be honest, 5 is pretty young f

I think like devnonymous says, SnapCircuits are a good choice. They aren't breakable and can be quite fun to play with. But, to be honest, 5 is pretty young for them to grok a whole lot. Most of this at this age is really about building something with you. You'll be doing most of the work, and they'll just be mastering the physical aspects of it. Don't try and explain or expect too much as it can be very frustrating to them. Mindstorms isn't really going to help much and Arduino / pi should wait until 7 or 8. Another good choice is Minecraft Redstone Circuits. Most kids love it and it provides an immersive way for you to build electronic systems together. (I run a program teaching kids coding + robotics in the bay area, happy to answer more questions if you have them! contact info is in my profile)