I don't think such title exists. Sure we have non-eroge titles but their stories still remain complex, suggests some psychological stuff or somehow simulates the dark sides of modern society (e.g. bullying, financial problems etc). Your best bet is to find OELVNs but I don't have much knowledge on that.
Though if you insist, the most kid-inviting title is Sengoku Rance. It's a great novel to learn a portion of Japanese History and some..... biology.