@Angela2851
As for the laundry, yep, it really annoys me when guests want to do laundry as soon as they arrive. I don't host guests with kids, so I can't comment on the need to do laundry after a long journey with a toddler. I mean I know that people with babies or small children seem to have endless laundry to do. The guests I've had who do this are just plain wasteful. They like to put on the washing machine (and mine is big - 8kg) for two t-shirts and two pairs of socks. The thing is, you are giving them free laundry services, and some people will take advantage of that, i.e. they will put on a wash for whatever they used that day rather than wait until they have a load because, well, they might as well. They're not paying for it, or rather, they are paying for your listing so they think they are paying for the luxury of daily laundry.
In your current situation, there is not much you can do about restricting use of the washing machine if that is something you have not already stipulated in your house rules. However, when it comes to the drying, explain that no dryer is listed as within the apartment. There is a clothes drying rack for their use and, if that is not sufficient (quite possible given the bitter weather we've had, but that's what my guests and are are still using), they can use the dryer at the laundrette on site.
Moving forward, you could put some restrictions in your house rules. Given that you have a laundrette on site, I would be tempted to specify that guests have access to this but that your washing machine is not for their use. Or, especially if you are renting an entire unit, limit the amount of use. That could mean that the washing machine is available for £X per load, if this is something you are able to monitor, or maximum one (or two) loads per week. Whatever you think is reasonable.
That doesn't mean you won't still sometimes have a struggle on your hands. Even when guests acknowledge the rules when booking, it doesn't always mean they think they have to follow them. When I still hosted short term guests, I introduced a rule that use of the washing machine was for long term guests only but that I could do a load for them (I am a live in host) for £3 per load. Some were happy to pay it, others not, but it did help to limit usage a lot. That rule is a bit moot now that I only host long term guests. I do still have to make a point of instructing them, e.g. please wait until you have a reasonable load, otherwise use the 'daily quick' setting, but some still don't get it. I recently added that guests were allowed to do one load a week. No one so far seems to have grasped that though!
@Kate867 's suggestion RE energy costs is a good one. It won't register with some guests, but it might help with others.