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Teach them the meaning of the symbols "+" and "=."  Then help them learn to write simple "number sentences" -- i.e. "3 + 2 = 5." Begin with horizontal number sentences.  Young children are already learning that they are supposed to write words and sentences "across" paper.  Following a similar practice with number sentences will be less confusing.  Once children have mastered this concept you may introduce the concept of vertical sums. "  Introduce terms such as "all together, "put together," "how many in all," "total," and "sum" that commonly indicate a child will need to add two or more numbers. Fact families show how the various numbers in an addition problem relate to each other.  Fact families often incorporate both addition and subtraction to help students understand the inverse relationship between these two skills.  The integers 4, 5, and 9, for example, are a "fact family," because 4 + 5 = 9; 5 + 4 = 9; 9 - 4 = 5; and 9 - 5 = 4. Consider using milk cartons to illustrate "fact families."  Cover cartons with paper, or a wipe-clean surface if you'd like to re-use the cartons.  Have students list the integers of a fact family on the top of the carton -- for example, 4, 5, and 9.  Next, have them write one fact from these numbers' "fact family" on each of the carton's four sides.
Familiarize children with addition symbols. Teach children the words that signify "addition. Use "fact families" to help children understand number relationships.