A day in Falmouth is good - the Maritime Museum is great and the 'vibe' in the town is much less hectic than St Ives, the seagulls are friendlier too.
Gardens of Heligan are SO worth a visit.
For more activity based day there's a new water park at Retallack which looks amazing (not been yet but def on the list for this summer!)
Pendennis Castle at Falmouth - check online (English heritage) before you go as they have jousting and medieval days during the summer.
Cornwalls' Crealys (rebranded as Camel Creek) is a fun theme park.
Otherwise just 'hanging out' on the beach is one of the best ways to spend a Cornish day - just about as far from hectic London life as you can get! Bliss.

Thank you so much - these sound great!

Lanhydrock National Trust is wonderful. Just between Bodmin and Fowey.

Also Polkerris beach is worth a visit (great sandy beach, shop, cafe for icecreams and pizza place for lunch if you can't be bothered with a picnic!) http://samscornwall.co.uk/)

Lappa Valley is fun, but a bit of a journey down the A30. Not sure if your 9 yr olds might be too old, but there is loads to do. Canoeing, climbing, train rides etc. http://www.lappavalley.co.uk/

Cardingham Woods is great for a long walk, paddle in the river with nets etc. Just north of Bodmin. http://www.forestry.gov.uk/cardinham

hope those ideas are a start. Our favourite part of Cornwall!

Hi there,
What are you best tips for a holiday in Cornwall in August with 9 year old kids?
We will be based between Fowey and Bodmin.
We've had some fab days out over the years: Camel bike ride, Minack theatre show, Tintagel, St Just in Roseland church, Port Isaac, Fowey, Watergate Bay (hotel + Fifteen), etc.
We've also done the Eden project a few times, but I am less of a fan (although it's handy for rainy days).
I am looking for more inspiration!! I know it's a hugely popular destination with SW families so am looking forward to reading about your experiences.
Many thanks
VdM