Just in case that you might be interested, Ore no Imouto.... (or or just OreImo in short) features super cute characters too (I'm using Kirino, the female lead of the series as my avatar here). However I'm not really recommending it for kids below 15, not because it's that 'dangerous' to them but due to the cultural differences between Japan and the US. You know, something that isn't wrong in Japan maybe deemed as "very wrong" in the west.