In a small saucepan, create a simple syrup by combining the sugar and water over medium-high heat. Stir until the mixture goes clear (it should only take a few minutes).
Place prepared strawberries and kiwis into a blender. Add in lemon juice and simple syrup. Blend until smooth. At this point you have lemonade concentrate like you'd buy frozen in a store. You can freeze yours for later use.
To serve, combine the lemonade concentrate with ice water to taste. The amount of water you use will depend on how strong you like your lemonade.