Do you have to have a level 4 house to have a baby on harvest moon magical melody?

No you don't have to have a level 4 house but you can get a level 5 house. If you want to have a baby with someone on it you have o get a second house or upgrade yours to a high level. After that, get 3 hearts on woody, Joe, or Kurt. that will unlock the double bed. hope I helped!- Ashlie