Hide call logs across user profiles

Access user profile and tap on More Settings (the second one in orange is child profile with Bom as name)

You will see yourself and child profile as below

Tap the cog icon on right and disable

Turn on phone calls and SMS

That's it.

If you enable, it gives you a warning that your calls and SMS would be shared as shown

Tested on stock 7.1.2

But the drawback is that child user can't use the phone or SMS

This is the designed behaviour

By default, only the primary user has full access to phone calls and texts. The secondary user may receive inbound calls but cannot send or receive texts. The primary user must enable these functions for others.

Note: To enable or disable the phone and SMS functions for a secondary user, go to Settings > Users, select the user, and switch the Allow phone calls and SMS setting to off

While it is not explicitly mentioned that secondary user will see call logs of primary user and vice versa, once the primary user enables then everything is accessible to secondary user (remember default is not to allow , if you do, there is a price to be paid )