Here is the flashcard series for adding 3. I use these for Gareth since Gavin isn’t really into the red dots. For Gavin, I use the Thomas and Friends addition flashcards and charts from ShichidaParents. If red dots aren’t inspiring your child, you should replace them with something that your child likes.
You can find more information on using the red dot cards in my series of blog posts on How to Teach Your Baby (the Glenn Doman way) or you can read the book “How to Teach Your Baby Math” by Glenn Doman.