My dad's account has been subscribed to Amazon Prime. I created a household with my dad and then I logged in to Prime video app on my phone. But I am not able to watch videos, it tells to buy prime. Where's the problem?
If you are currently marked as a "child", you won't be able to watch prime-movies. Recently, Amazon introduced the "Teens" category which supposedly will allow you to access "certain Prime benefits" (which is said to include "Prime Shipping, Prime Video, and Twitch Prime") This also is limited to children 13-17. Also, they make note that teen-logins are not currently supported by kindle... so that might also be problematic for some.