Well you better replicate it on unmodded version
Viewing post in Slave children still bugged in 10.0a
Only mod I have installed from the revamp is the marriage one, but that does supposedly make all children heirs, so that may be conflicting with it but I can give it a go, and if anybody else replies meanwhile who'd not using a mod and can either confirm or deny the veracity of my speculation, then they'll likely provide either a similar issue or confirm it's the mod providing issues. I'll start a new game with the mod turned off and get back to you.