Many years after adopting FirstChildRedirect and making it suitable for use in MODX 2.1+ (!), I’ve just made available a new version of FirstChildRedirect that’s confirmed to work in MODX 3 as well.
This release bumps the minimum PHP version to 5.4, but you should really use 7.2 or up 
Brought to you by a train ride heading to the SnowUp in Switzerland.