Pgrep for processes which are not associated with a terminal in Ubuntu

I would like to find all of the PIDs of processes which are not associated with a terminal and started by CRON.

When I do the ps aux | less command, I see in the TTY field a lot of processes with ? character

I would like to get those processes ID, is there a way to do that with pgrep?

I tried looking at the documentation but it's not very clear...

CRON jobs are never associated with a terminal, but there are processes without a terminal that are not CRON jobs.
Find the PID of the "cron" daemon

pgrep -o -x -u 0 cron

Now find the PIDs of its children

pgrep -P <pid_of_cron_daemon>

All in one

pgrep -P `pgrep -ox cron`