Counting and Measuring with Lego: Preschool Maths Game - Good way to visually compare numbers - I would suggest making the corresponding numbers (like 5 and 15 or 8 and the same color to help see the pattern relationship between the numbers and 15
Attendance as they walk in! A quick get to know you/math (counting and graphing) activity. Later in the year students can generate the questions and write them. Place on light colored paper, laminate, and questions can be added with white board marker.