Facetime for child Apple ID account
I created an Apple ID for my child (under 13), added that to my family sharing account, created a user account for him on my MBP, had him log onto his account on the MBP, fired up Facetime and had him log in under his Apple ID... but he can't make calls. What am I missing? I see articles about enabling FT for iPads and such, but can't find analogous setting on my MBP.
iMac 21.5", macOS 10.13