How do you get the child pid of `unshare` when using --fork for `nsenter -t <pid>`?

When using unshare --pid --fork, the nsenter command must attach to the child pid not the unshare pid to get to the right pid namespace. I can get unshare's pid as follows:

unshare --pid --mount --fork --mount-proc  bash & 
echo PID: $!
fg

but I need unshare's child's pid (2914003) to enter the right namespace:

ps wwfuax | grep -A1 unshare 
2914002 pts/4    S      0:00  |           \_ unshare --pid --mount --fork --mount-proc bash
2914003 pts/4    S+     0:00  |               \_ bash

This works: nsenter -t 2914003 This does not: nsenter -t 2914002 I was hoping for some kind of option like unshare --show-child-pid but there isn't. What is a nice reliable way to get unshare's child's pid?