Question Author
Thank you for your answers. However, maybe I should give some background information.
We live in Belgium and, together with our granddaughter's parents , are bringing her up to be bilingual in French and English, working on the one parent, one language basis. With her father and outside the home, she is exposed to French and this is her dominant language. With her mother and when she visits us, we speak only English.
We have a little app for number games which she enjoys and is clearly learning from it so we were looking for something similar for letters but with a British English voice. All her books here are in English and she likes having them read to her. She likes songs such as Ten Little Monkeys Jumping on the Bed and, recently, has started singing that spontaneously alone.
The idea is definitely not to use a smartphone app as a substitute for books or personal interaction, just as a fun addition.