No boots no care. Does your contract mention outside time? If so, the child needs to be dressed for the weather...regardless of walking status. They can buy a pair of Stonz or similar "boots" that are meant for non-walkers but the child needs to have his feet covered.

I'd give the parent a firm date (2 days max) to have boots by or the child will no longer be accepted into care as lack of boots prevents all children from enjoying their day. If the boots are not present at drop off the child returns home with the parent...make this very clear in writing and verbally.