Buying android app on Google Wallet for child?

I'm really hoping someone can help me with this. My child has just had a birthday and we bought them a Tesco Hudl, so they can play Minecraft.

Minecraft cost £4.99. I'm really unhappy about putting my credit card details into the Hudl. I don't want my card linked to their googlemail address.

So how do I pay for the app? I have tried loading it on my PC, but it asks me what android I want it on and the Hudl is not listed. If I enter my Google account into the Hudl so I can download Minecraft will I then beable to remove my Google account.

The only other way I can see to do it is to buy a gift card at £10, but I would rather not do that.

How do I add pay for Minecraft for a different user. I can't be the first person who has thought it is not appropriate for their financial details to be on the child's tablet?

Buy a Play Gift Card instead.

Is the only way to do this is to buy a play gift card? Is it possible to buy a £5 play gift card?