Various interactive activities.
This site allows kids to explore decimals on a number line, which makes it really easy to show how to round up or down.
Choose Proper Fractions (Easy) for this skill. The hard version would be a great extension. Both go beyond the benchmark fractions.
This is a great site for modeling perfect squares and other numbers by using arrays. It shows the equations so kids can see that a perfect square only has one while other arrays have two (commutative property).
Click the hardest level for ordering decimals.
This is a good game for practice with ordering decimal numbers. You should preview it before you share it with kids, however, as Builder Ted's pants don't fit too well. When I used this with my kids we just talked about whether they could be mature about the British humor, and it wasn't ever a problem. Select Level 1 as 2 and 3 have negative numbers.