Robux help from giftcard

Goodfellows24

Have just bought 2 giftcards, read instructions and went onto roblox.com/redeem. I entered the codes and bought my Robux. How do I get these put onto my childs account? She is on a amazon fire tablet. Thank you for any help, have messaged the help on Roblox, but unsure how long the replies usually are. 

PHK

You are supposed to log into her account and add the gift cards. 

marcia_

 You may have just wasted your gift cards because you haven't redeemed them through the childs account 

Goodfellows24

I had that horrible sinking feeling..... because I have not done this before it said log on on a computer, which of course was me not the child. Thank you for your help