Helmets r us has been a good source for cheap helmets (rated helmets starting at $4 for non-profits).  I've known of a few sources for free helmets in the past, but those I'm aware of have moved onto other health related causes.  
Otherwise we use sunlite ulocks via JBI bike (aka j&b) which cost about $6.5 (up from 4.50 from our first big order).  We've also gotten a ton of lights on their close out list which we provide if necessary.  Their kidzamo line is a knockoff of knog's style and cost on front or rear lights is $3, as I recall.  
Hope this helps someone, but would gladly have a different source for any of the above!