Very young children build the foundation of their math skills by learning to count. Constantly count things with your child, for example, when putting on her shoes, note she has two feet and help her count them by saying, "Look, you have TWO feet. See, one and two!" As she gets older, play counting games by asking her to count the stairs going from the lawn to the front door or the number of birds on the front porch. Introduce the concept that number names reflect the amount of something by counting the objects and then removing or adding one and counting them again.
As she begins understanding that the concept of written numbers encourage her skills by playing numeric "I Spy." Tell her you spy the number eight, show her what the number looks like on a chalk board if she's unsure, and help her look around the room to find that same number on a block, clock or book. Play this game when out driving using speed signs or at the grocery store using pricing displays. When she correctly identifies the number, hold up that same number of fingers and let her count them so she learns to connect the number symbol with a specific quantity.
Strengthen your older child's understanding of fractions by writing down a doubled version of a sweet treat recipe. Explain that to bake the dish correctly, he must divide each of the ingredient quantities in half. Attach easy-to-read stickers on measuring cups or spoons so he's not frustrated trying to read tiny or faded numbers. Have him write down the correct quantity on the recipe sheet after halving the amount. For example, if your doubled recipe calls for 1/2 cup of sugar, he would determine the halved amount, cross out 1/2 and write 1/4 in its place. This game works best for children who already understand basic fractions but could benefit from further building their skills.
Pique your child's interest in math by showing him pictures of toys or other desirable items and let him calculate how many weeks worth of allowance he'll need to purchase each item. Paste a sticky square to each picture and give him a piece of paper and a pencil. Turn the actual prices into whole numbers on the sticky sheet his allowance divides in evenly, unless he's comfortable with more complex division.