If you see that your toddler appears to be interested in letters and books, buy him toys consisting of letters, such as magnetic letters or foam letters for the bathtub. (verywellfamily.com)
Then, I looked and saw our daughter splashing happily amidst foam letters and animals in the bathtub. (diaperjunction.com)
I have large foam letter stamps that I like to use on projects like this, but stencils would work perfectly, too. (adirondackgirlatheart.com)