Unless your child is begging for worksheets, just make it play. At 3, DS was playing yahtzee, and other games that use adding dice, plus checkers, blocks (including Cuisinaire rods), connect 4, etc. He'd count things a fair amount and tell me the relationships between the things he'd counted. We'd make tally marks in groups of 5 to keep track of speech therapy exercises. DS also started to take to maps at the time, so we read several books about maps, took the hiking maps from every local park, and bought him a compass. He was also learning to bake, doing a lot of doubling and halving recipes with me. Living in a house where all members are quite mathy, learning the math has come quite naturally through play and general living.
If a child is asking for something more structured, then provide it as appropriate, but if a 3 year old is just showing a talent for numbers and a love of all things math, do it in an age appropriate manner.
