Here's a nice post on using place value cards to help students understand decomposing numbers and expanded form. Includes a link to a set of place value cards. Could change colors to go with Math-U-See.
Two preschool math activities using Duplo Legos. These are great for younger brother while the older ones do their schoolwork! Identify the next number in a series of numbers up to ten. Pre-school age 3 and 4