I don't have the age restrictions you do but my policy is :-

Older child remains in FT care. They may attend on a part time basis but fees are due for the FT space for the older sibling. If and when a space opens up, the parent on mat leave gets first refusal of that space but they are expected to pay for it. This means, they are paying for two FT spaces. One that the older child is using and one that is being held for their younger child.

Should a parent not wish to pay for the second space normally because it opens up long before they need it, then that vacancy is advertised in the normal way and they risk not having a second space when their mat leave ends.

I do not accept part time children. It normally results in a loss of days that I am both unwilling and unable to absorb. This is especially true during mat leave if a parent wishes to reduce the days the older child attends because it often goes hand in hand with the expectation that those empty days are available for them to return to once the year has passed. I cannot and will not lose two days income for a whole year so a client has the peace of mind of knowing they have a FT space available to them. The reality of finding a new client who wants the exact days that a PT'er leaves empty are slim esp when you add in that after 12 months, the space is going back to an existing client.

Here they have two choices - pay for the space the older child is in and also pay for second space if one opens up for the younger child or leave and hope for two spaces at the end of mat leave.

Simply, I cannot absorb the costs of their expanding family with regards to two spaces, by allowing a drop in days for the older child and also in keeping a second empty space for potentially months, so they have the peace of mind in knowing they have two spots.