Continuously monitor a process and all its children with `top`?

I want to run a process that spawns children, e.g.,

for i in {1..4}; do
  sh -c 'echo $$; for j in {1..3}; do
    sh -c "echo ...\$\$; sleep 1"
  done'
done

and I would like to monitor the CPU and memory usage every 2 seconds with top. - I can monitor its resource usage with top -p , but this doesn't account for the children. - I can monitor _all_ running processes just with top, but this is too much information. - I can precompute a list of PIDs, then pass all of them to top, but the process could then spawn new children, which would not be accounted for. How can I get a top snapshot every 2 seconds of just the process I'm running and any processes it spawns? Someone asked a similar question [here](https://unix.stackexchange.com/questions/178795/how-can-i-find-the-cpu-resource-utilization-of-a-process-and-all-its-children) , but it was about summarizing this information into a *single* number, after the process finishes. My question is about *continuously* monitoring the processes while they’re still going.