Savage Sagana Camp is primarily the location of the Savage Wilderness Safaris (http://www.whitewaterkenya.com/) white water rafting operation, where rafters get their pre-trip briefing before setting off on river adventures. It's also where the rafting trips end.
The site is open to non-rafters who want to enjoy being by the river - its a green oasis with an extensive area to camp with your own tent; several BBQ locations are dotted around the site and there are nice clean toilets and showers. For a little extra, you can stay in either a tented banda or a basic banda (=basic cottage), with its own bathroom and shower. If you don't want to be catered for food-wise, bring a stove and cooking equipment (even in the cottages/tented bandas which have no cooking facilities) and you are free to do your own thing.
Its only 1.5 hours from Nairobi on the main Thika Road (between Thika and Nyeri), and it's very affordable. There is a small swimming pool. The whole place is very child friendly.