For a spot more than 6 months away I would just tell the family that basically they are looking too soon and that in our area at least there will always be people with spaces. Also because most parents are only required to give a 2-4 week notice many good caregivers won't even know yet that they will have spaces for April. They can safely wait until January to start the intensive interview phase of their daycare search so please feel free to contact me back in January to discuss your needs.
Too often they have second thoughts that they grabbed something too quickly and then over the next 6 months find out they had other alternatives and rethink. Which leaves us having taken a hit in the pocketbook and still having to readvertise when we should have just kept advertising and trying to fill the space when it was available.
The only time I would seriously consider this is if I knew I had a space such as a maternity leave coming up or in the summer for kids starting school.