I don't understand why the charity is telling you the amount of rent you can charge. Normally, you as landlady would decide the amount you wanted. Is the rent being paid by Housing Benefit or is the charity paying it in some other way? If it is Housing Benefit then the local Council decide the upper limit. As others have said, rent is just for accommodation & (unless there is some other arangement with the charity) you can ask for a separate payment for the utilities etc. You would not expect to get more rent for the same amount of accommodation (i.e. 1 room) just because there are more people living in it, so I find it strange that the charity says the payment would be higher if there was a 3 year old with the mother. This implies the payment is intended to cover something other than rent for accommodation. I suggest you talk to the charity to clarify & fully understand what the position is.