If you're looking for something to do on Saturday, here are some suggestions.

Porthkerry Country Park - 220 acres of woods and meadowland leading to a pebble beach and spectacular cliffs. There are nature trails, woodland walks, orienteering paths, a cafe (only open in summer) a small adventure playground, a stream and a mini golf course. Something for everyone.
The park rangers run a Wildlife Watch group which meets for two hours once a month, and the next meeting is Saturday 18th October. It is aimed at 8 to 12 year olds, but it's worth asking about younger ones. (The photo on the website seems to have parents and littler children)
See the website : Porthkerry Park
or contact them by email : porthkerry@valeofglamorgan.gov.uk
Waldorf Inspired Needle Felted Elf atop a Pumpkin
Originally uploaded by Nushkie Design
Also on Saturday is the Cardiff Steiner Harvest Fair. This is at St Catherine's Church Hall, Kings Road, Canton, Cardiff, from 12 to 6pm. Carve a jack-o-lantern, buy some hand-made crafts and celebrate the harvest. Free entry.
See the website : Cardiff Steiner