Your post doesn't really make your issue or question very clear.
What exactly does "Trying buy data" and "Sim updating child's watch with Data" mean?
If you want assistance from the Community Forum then you need to explain your issue/question clearly and in detail.
If you're using the €12.99 plan then there's no need to buy additional data as it comes with unlimited data.
What exactly are you trying to do, what steps are you taking to do it, what problems are you encountering, what error messages are you getting etc.
If you need to contact 48 support about this then see the links in my signature below.
