If you want to help your child to understand numbers (and not just get a superficial, hazy and shaky notion of 'sums') and to have fun doing it then forget those pricey 'educational' electronic gizmos at five times the price and buy these.
I used these wonder blocks more than 30 years ago when teaching infants and juniors with learning problems and now I use them with my grandchildren. In my view there is no better way for young children - or even adults whose grasp of number is shaky - to truly understand the link between symbols on a page and the real, practical numbers they represent. And they can be fun in a creative way too: playing with them to create shapes and patterns helps develop the bases of all real maths.
Children need to reach a certain stage of brain development (about the age of 7) before they can really understand the abstract ideas behind adding, subtraction, multiplication and division. Until then they simply have to remember HOW to do the processes without any real grasp of why. This sometimes even confuses very bright children who find it distressing simply to follow procedures they don't really understand. But the more experience children have of handling numbers in concrete, tangible forms the quicker (up to a point) they will understand and the more solid their learning will be. And they will gain huge confidence when they finally understand why 'sums' work the way they do.
Remember, even adults sometimes need concrete objects to tackle abstract ideas. Think about it: have you ever used pens and coins, etc., to illustrate an idea? Or perhaps, if you are a man, resorted to using concrete objects to explain the offside rule to your wife? (Or maybe to understand it yourself?). ;-)