The book How to Teach your Baby Math, by Glenn Doman, recommends teaching babies/toddlers numbers by showing them cards with dots on them, one at a time, whilst saying aloud the number of dots.
Instead of making your own cards and using your own voice, you can run this web app and use your smartphone and thumb.
The initial screen is blank. Tap anywhere on the screen to show some dots and hear the number. After about a second, the screen will again be blank, ready for you to tap again.
The URL above will show numbers from 5 to 10. Change the numbers at the end of the URL if you want a different range.
If you want to host this yourself, or improve it, you can find the source code on GitHub.