Give the children problems to work out. Use the different language subtract, minus and take away.
If you they have 10 sweets and you ate 2 how many would you have left?
If they had 8 sweets and you ate 3 how many would you have left.
Model the number sentence by writing it on the white board for them.
Get them to record one problem with pictures and crossing out and with a number sentence. If they write a number sentence make sure they have the understanding and can read it out to you. If they are struggling then the pictures will be more meaningful.