Is it harmful to breath in propane fumes my neighbor downstairs has a leak cause that's all I smell they have a one and seven year old children?

Get Help!! Yes, it can be harmful to breathe propane but not as harmful as being in the house or nearby when the accumulated propane explodes. Alert your neighbors right away of the danger of the propane leak. If they don't listen or care, then call the fire department but stay away from that leak until he fixes it and if they continue to expose their children after that, call child protective services.