Block access to google for younger kid when logged in on mac but make sure it works for everyone else. Run on root's crontab every minute and make sure common_hosts contains what you want as baseline hosts file.

block_goog.sh

cd "${0%/*}"

# Check which user is logged in
user=$(stat -f '%Su' /dev/console)

# Check if hosts file contains 'google'
if $(grep -q google /etc/hosts);then
    GOOGLE=true
else
    GOOGLE=false
fi

# Add google if it doesn't exist and user is Kylie
if [ $user == "bobby" ] && ! $GOOGLE; then
    cat common_hosts > /etc/hosts

cat >> /etc/hosts << EOF
127.0.0.1	google.com www.google.com
EOF

# Else, clear it out
elif [ $user != "bobby" ] && $GOOGLE; then
    cat common_hosts > /etc/hosts
fi