What happens when there is a siren past eight p.m.

I have succeeded the past two nights in getting the boys to leave me
alone after the last bedtime kiss - I will not return upstairs. They
have everything they need and can get back in bed by themselves if
they get water or need to pee. So what happens if there is a siren
outside after I've left them in their beds? I hear small feet get out
of bed and trudge across the room heading for my bedroom window, which
looks out to the street. After the siren has passed the feet take
their three-year-old owner right back to bed.

--
Jessica