Here is a little hint to use when doing addition sums without props or pictures. Use the number grid. The first number in the addition sum shows you where to start on the grid, the second number shows how many jumps to achieve the answer. The answer to write is the number you stop on.
EX: 5+3= __ (5 is where to start, place a counter on number 5, 3 is the jumps needed to achieve the answer.)
Encourage to count the jumps (1, 2, 3 jumps) and not the numbers they are jumping on, as then the children will get mixed up. Hope this hint helps you when the children have addition sums for H.W. Happy Adding :+)