Chapter 1~ Place Value, Addition, and Subtraction to One Million
http://www.math-play.com/place-value-games.html
http://www.math-play.com/Rounding-Numbers-Pirate-Game.html
http://www.ixl.com/math/grade-4/subtract-numbers-up-to-millions-word-problems
http://www.factmonster.com/math/numbers/rounding.html
https://www.mathsisfun.com/rounding-numbers.html
https://www.ixl.com/math/grade-4/rounding
http://www.abcya.com/rounding_numbers.htm
http://www.math-play.com/rounding-numbers-pirate/rounding-numbers-pirate.html
http://www.math4childrenplus.com/rounding-numbers-rally-game/