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!
Could attach the letters of Toddlers names to these and see ifthey can make a tower spelling their name Preschool Letter Recognition Activities - Matching Upper and Lowercase Letters using legos, and other fun activities.
Printable block letters... and over 150 ways to fill them
Letter Hunt for Early Literacy: A sensory literacy activity for toddlers and preschoolers learning the alphabet. Ages 18 months ELA 2 Demonstrate awareness of the alphabet APT 2 Demonstrate flexible thinking during play
Find the Letter & Swat It! Active Way for Learning Letters!