Doing math in your head (like the Germans) is easier if you think in blocks of 10. Here's a fantastic graphic for school kids that can help you build up the skill of doing math in your head. (I couldn't do it until I moved to Germany and learned the metric system--now it's quick and easy for me to do math in my head!)
Math Play: 20 Minutes a Day (Blog Post) Can we encourage math play for early childhood the same way we encourage 20 minutes of reading per day? Imagine the authentic number sense that we would develop in our children.