I'm not entirely sure specifically as it could vary. But generally, a visual novel often involves a story with characters and plot developments presented in a visual and interactive way. 'Kodomo no Jikan' might center around stories related to childhood perhaps, with characters experiencing various events during that time of life.
Probably not. It depends on the content of the visual novel. If it contains complex themes or some mild forms of drama that might be difficult for very young children to understand, it may not be suitable for all ages.
I'm not sure specifically what 'Cap deage' means. It could be a very specific term, a misspelling, or something relatively unknown. It might be a proper name, a local term in a certain area or a very niche concept.
This 'isekai de saikyou maou no kodomo novel' could potentially be a story full of fantasy elements. The 'isekai' setting gives the opportunity for a unique world - building. With the main character being the child of the strongest demon king, there could be a lot of political intrigue. Maybe other characters are trying to use or manipulate the child because of their lineage. Or perhaps the child is trying to break free from the expectations set by their father or mother, the demon king, and wants to create their own identity in this strange new world they've found themselves in.
I'm not sure where you can specifically get this light novel. You could try checking some popular online bookstores like Amazon or Barnes & Noble. They often have a wide range of light novels available.
I don't have enough information to say exactly who Cap'n Kathy is. She could be an original character created by the fan fiction writer. Maybe she's a pirate - the 'cap'n' part could suggest that - who has some connection to the wizarding world of Harry Potter.