For some of us (myself, and obviously you), but not everyone, that setting has been relocated. The pet thing, child-okayness, and a few other things, all of which are admittedly more "rules" than "amenities" are now found under Booking, as part of the House Rules section. Makes sense, but it would've been nice of AirBnB to include a note about that in the Amenities section for at least a few months.
Other readers -- note that this change hasn't been rolled out fully yet. You might still find this setting under Amenities and not under Booking. Thank AirBnB for the confusing inconsistency. 🙂
If you find this helpful, consider clicking the Thumbs Up button near the lower right. Thanks!