If your child was working on one less and one more then have a go at showing them a group of objects. Get them to count out the objects. Say you are going to take one away (there is going to be one less). How many do they think will be there? Repeat this, try one more.
If your child was looking at the difference then remind your child about what we learned yesterday. Recap finding the difference by using objects to count this out (Lego, blocks, pasta etc.). Show your child a number line a work through using this to find the difference between the numbers. Try this with 1-5, then 1-10, then 1-20.