Researchers have found that children who start school understanding mathematical concepts, or having 'math sense', will continue to outperform peers through 7th grade on basic core math skills needed to function as adults (Geary at University of Missouri). What this means is that parents can informally give children this advantage in everyday experiences. Statements such as "cutting the sandwich in half," four toy cars represent the number '4', a gift box is a 'rectangle', or counting each item—"1 car, 2 cars, 3 cars..."
There is a place for rote counting, but counting actual objects helps give children what educators call 'number sense'.
Activities at home can naturally lead to a math focus: counting plates or glasses the child puts on the table, counting the number of sticks picked up in the yard, or counting the number of blocks put away.
Children's literature has so many wonderful number books (Mouse Count, Ten Little Caterpillars, The Very Hungry Caterpillar, One Less Fish, The Doorbell Rang) which are great to add children's math and reading experiences. These need to be read with pauses for children's predicting and counting.
Flash cards are less meaningful as they are removed from context of the real world. Also, children easily understand your value and attitude towards a subject, so if you did not like math in school—your child can 'sense' and may identify with your feelings.
My last piece of advice—enjoy math experiences with your child. Math is everywhere!