Let the children understand that there are 10 sticks in a bundle, and we can untie this 10 stick. This is because children will find that there are 10 sticks in 10, 10+3 = 13. The child can see at a glance how many bundles are left, and then take two more bundles from the remaining bundles. This is the number. This method is called breaking ten methods. I hope it works for you.