@Mcreggae
For a 10 and 8yr old,depending on how 'mature' they're..most kids places might be a boredom haven especially if they have to share facilities/games with kids who're below 6yrs. So,other than the games oriented places mentioned by @Djinn et al...maybe you could try out 'wanyama' places. e.g
Safari walk - 100(adult) and 50(child)
Orphanage - 100(adult) and 50(child)
Giraffe centre - 100(adult) and 20(child)
Sheldrick elephant orphanage(no standard fee,you just leave your donation while exiting) but viewing and interacting time with the young ellies is strictly 11am-12noon daily. A very good experience for kids!(am sure you've watched the ellies on 'Elephant Diaries' KTN,every Thursday at 7:35pm)
In terms of games oriented...I would vouch for Splash,anytime!
BTW,you can combine splash with any of the above since they're along the same road i.e Langata Road...
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