Some suggested wording:

Get ready to blast-off! It's Pedro's 4th Birthday! Saturday 27th May, 1-3pm at 24 Blaidon Street, Rose Bay RSVP Ellen on 4563 9856 by Nov 27 OR Come and celebrate Harry's 6th Birthday Sunday December 4, at 1pm at 23 Crown St, Blackhaven RSVP Cassie on 96