A good learning project for yourself, it looks like you've combined a lot of technologies together to make this game possible. Good job, very well done.
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Littered with advertising and in-app purchases, I don't consider this practise as safe for children as they can easily make purchases and navigate into 3rd party adverts without much blocking.
Generally, I don't think your goal should be to get children to tap on adverts (three of my adverts were for Uber, a cellphone network provider and a bank). You likely don't have control over this content, but your highlighted quote is about it being child safe and - in my personal opinion (and it is my personal opinion) - I don't consider this a factor for this game.
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When popping the bubbles there is some slow-down (maybe pre-cache the audio effects so they don't reload from disk each time a bubble is popped?).
There's some aspect-ratio related issues; the game screen is slightly squashed, however there is a massive empty margin underneath the advert at the top so I suspect this is the advert causing the content to get squashed downwards.
Noticed a UI bug where hitting the ambiguously labelled "No" option after hitting "Play" caused the app to loop between hitting "Play" and "No" over and over.
Quitting sent me into a loop of re-opening the game and quitting over and over.
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The game-play itself is very generic and uninspired. There is not much of a theme, either. Artwork is great, but I understand that most of the artwork came from a free online-resource. I am grateful that you included a credits page, you were very upfront with where the assets came from.
The icons, fonts and text are a mish-mash of styles and do not feel consistent to each other, let alone a theme. These stand out from the other resources, such as the monsters, stars and backgrounds.
The name "tap!" is not very competitive and is probably the most common name for a mobile application you can find.
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Two star rating reflects the stability of the game and the fact that the game itself does work perfectly fine, as intended, and from what I can see the execution goals of the developer have been met.
Definitely looks like a learning project; it reminds me very much of my early mobile games back when I was working at a small games studio. I think it was a mistake to have this as your debut project.
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I noticed you changed my copyright message from my Android run-time; this is fine, but it comes across as rather scummy as it is modifying my company's copy-right notice and replacing it with your own.
If you don't want to credit my company for the work it has done to make your app possible then you should remove this message entirely, I am okay with that as it currently has no license attached to it, however this code is not public domain, the copy-right is still under my company as original author, so modifying the notice comes across as a scummy thing to do (it comes across as if you're claiming credit for the work I've done, that's worse than just removing the notice, which I am fine with).
You now have a place in the credit section. You were 100% correct, this is basically a learning project for myself. The game is much more kid friendly when the advertisements are removed but I suppose the in-app purchases are not kid friendly.