Certainly Social Services would want to get involved if the child is under 10, but they may wish to investigate the background circumstances of any child under the age of 16. Since such behaviour from children towards adults is an indicator that the child may be at risk of some form of abuse.
The child comes first in this situation, being insulted by a minor is not nice, you should report the incident to the Police, so they can compile evidence towards an ASBO / CRASBO, if the insults are of a sexual nature, then report this to the Police, and Social Services, to protect the minor.