Pigeon nesting on windowsill

Hello, 

We arrived back from a week's holiday to find a pigeon's nest on our windowsill, on our first floor flat. Before leaving, we had noticed pigeons perching on our windowsill, but hadn't realised they were building a nest, or at least scoping it out.

The nest has one egg in it and we'd like to give them every opportunity to complete their breeding cycle.

The nest is outside our bathroom window, so we will need to use the room. We also have a toddler and a three month old baby, so while we will do out best, it will be hard to keep the noise down. 

We are looking for any tips that will allow us to use the bathroom without disturbing and startling them at the risk that they abandon the nest.

Also, any thing else we need to be aware about pigeons nesting on our windowsill (i.e hygiene, attracting pests, etc.).

Thanks