What is happening here?
Problems like 47 + 8 or 62 − 5 cross a full ten. Your child knows the principle from grade 1 (8 + 5); now it has to work anywhere up to 100.
Children often get the ones right and lose the ten along the way: 47 + 8 turns into 45 or 65. That is not really an arithmetic slip, it shows that the step across the ten is not yet secure.
What helps at home
The route is the same as up to 20: first fill up to the next ten, then add what is left. With 47 + 8 you ask "How many does 47 need to reach 50?" (3). That leaves 5 of the 8, so 50 + 5 = 55. For subtraction, step back to the ten first: 62 − 5, take away 2 (60), then 3 more (57).
Let your child say the steps out loud. Two or three problems a day are plenty. It matters more that the step across the ten is always the same than that it is fast.
What can go wrong
If your child simply counts on (47, 48, 49 …), the answer is often right but the way there is slow and error-prone. Going back to smaller numbers is not a step backwards: a child who crosses the ten confidently in 8 + 5 can carry that over to 48 + 5.
The hundred chart helps to make it visible: one step down is ten, one step to the right is one.