A deceptive sign often seen in residential neighborhoods,
intended to warn motorists to drive slowly because of the
presence of children, but often humorously misconstrued as
indicating the neighborhood youngsters' lack of agility. Though
made to give the appearance of official traffic signs, "slow
children," or sometimes "slow children at play" signs hold no
legal weight.  Studies have shown that these signs don't
decrease the average speed of traffic through neighborhoods
where they're installed, so their efficacy as a safety feature
is dubious. At the very least, signmakers should insert a comma
to eliminate grammatical ambiguity. An alert driver will usually
be able to maneuver safely around slow children. It's the fast
ones that you can't see in time to avoid.  information from
http://www.ci.phoenix.az.us/STREETS/atplay.html