Use flashcards. Make multiplication cards for each number set. Although this may seem tedious, the process of making the cards will actually help you to learn them. Once you’ve made them, spend some time each day studying until you know them all. Focus on one number set at a time. When you go through the cards, put the ones you get wrong back into the pile so you see them multiple times.
Get some addition practice while reading picture books together. There are a ton of great picture books that have overt and hidden addition facts and practice, but you can turn any book into a lesson in addition. If you read a page with a picture of a forest, you might say to your child, "I see three trees and four flowers. How many plants are there all together?" You can add characters, shapes, items, or anything in multiples.