T.V.
K.,
Do you have a fenced back yard? If not bring your 4 year old in the house when YOU canit watch him. If you are paying one of the teens to babysit, then that's a different story. And as for the honor students, athlets etc....still too old for a 4 year old to hang out with. You might consider some play groups with kids his age and meeting some moms that might be interested in trading some Mommy time outs for each other.
Your own words:little gang bangers/thugs/losers
If something happened to your son, you could be turned in and arrested for child indangerment. Your little guy has NO business hanging out with this group.