Buying apps - how secure is it?

[roundabout1]

I have a new Galaxy phone & would like to buy a few apps the easiest way is through Google play store but am a bit worried about my credit card details on there. More worried about my dc's buying things by accident (or deliberately!) without me knowing. Does anyone know if I need to log in before purchasing anything? Thanks

If I buy anything from the store, I have to log in with my gmail account. I've had my android for 18mths now, and haven't had a problem with buying apps this way.

Galaxies are fab

Thank you!