AN INTRODUCTION to the orchestra - children playing for children is the title of the Royal Irish Academy's Saturday morning sessions for children aged four to 14. The one-and-a-half hour musical experience is presented by James Cavanagh, professor of conducting and orchestras at the academy. There will be sessions this Saturday, November 16th, and on Saturday, November 23rd, at 11 a.m. The cost is £5 per person. The academy recommends that very young children be accompanied by a parent or guardian. For further information and booking please contact the general office, RIA (tel: (01) 6764412).