Premium removes ads. If you see ads after paying, the app is not seeing your subscription on this phone.
To fix it, see I paid but Premium isn't unlocked.
With Premium, you may now and then see a card on the main screen that says New from KidPlay. It tells you about one of our other apps. It doesn't mean Premium is off. Tap the X to hide it for good.
If you joined the account of someone with Premium, you get Premium and no ads through them. Make sure you are signed in.
Open Help in the app and tap Contact us. Tell us the email you are signed in with.