I have to say that I'm a bit concerned here. A loft ladder is not going to be designed for constant use, nor is the loft, even if boarded over. Loft timbers, unless strengthened are designed to take the weight of the ceiling, plus access for maintenance, and for light storage only. then there is the safety aspect of an unguarded hatch opening. Unless you have a proper loft conversion, in my opinion using as a playroom is not an option.