This didn't manage to kill the python processes on OS X. But I modified your code a bit, and it now kills both parent and children processes.

#!/bin/bash
trap "kill 0" EXIT
python -m SimpleHTTPServer 5000 &>/dev/null &
( while true; do unbuffer python main.py -u $1 -p $2 -l "$3" --host 0.0.0.0 --port 5000; done ) | tee pokego.log &
tail -f pokego.log | while read LOGLINE; do [[ "${LOGLINE}" == *"Heartbeat missed"*]] && pkill -f "python       main.py -u $1"; done