Register form android app using AWS cognito

I'm building a register form for an android app. Now I don't want to give users the ability to login using Facebook or Google, but I do want to use Cognito to provide a secure connection to the dynamo database.

The main reason I don't want to use facebook or google is because I want to give children, who don't have a facebook or google account, give the ability to register simply by entering an username and password.

Now as far as I understand, I can use my own database with users to connect with cognito:

But I do not want to configure and secure my own web server with database where I store my users. The main reason I want to use Amazon in the first place is because it's secure and I don't have to build my own complete infrastructure.

So does anyone know or there is a better way to still use cognito and dynamodb, and giving users the ability to register without any of the existing services like Google or Facebook.