To add a level of difficulty. I would add number cube to see how many letters to cover up at a time. Use tally marks, dots, numerals ect Free "find the letter" alphabet worksheets! Get them for uppercase, lowercase, and both!
By 24 months, children should be able to imitate drawing vertical and horizontal lines, as well as circles and v shapes. This is a great worksheet to do with your 2 year old after you have read the book to develop their fine motor skills!