How can I disable/lock Google Play on my phone(may be restrict it with a password)? I tried this way and followed the steps given there. But it's not asking any password for free apps.
It won't ask for a password for free apps since there's no danger of financial loss of any kind, it is a good point however
There are apps on Google Play that can 'lock' certain apps check 'https://play.google.com/store/search?q=app+locker' or something to that effect
This one looks like it does the job: https://play.google.com/store/apps/details?id=com.domobile.applock&feature=search_result#?t=W251bGwsMSwyLDEsImNvbS5kb21vYmlsZS5hcHBsb2NrIl0.
They will enable control of apps via a pin
From google play download applockr or you can disable the app via settings>apps>all applications then by selecting the google play application and pressing the disable button to disable it until you want to enable it (do the same process but the disable button will be replaced with the enable button)
I think the explanation on this post is what you need: http://www.android.gs/block-google-play-android-market-from-inappropriate-downloads/