This is a hard one for me. You have to consider 4 siblings, for 5 days in a row. Siblings are hard on each other and may be more of a hassle then it's worth.

Also, I have trouble understanding how any family can afford $600.00 in child care for one week. So I would be cautious as they may be looking for discounts and cutting corners wherever they can.

AS far as the deposit, I would take 2 weeks and apply towards the last 2 weeks of care. (so that gives you a months notice if they bail)

Really, we should be charging a premium for siblings. They're high risk! If one goes, they all go. If one get's sick, they all get sick. If one has a bad behaviour or habit, the next one will probably develop the same issue.