What is the number of US children (and percentage) who attend day care?

Some children attend day care 4 or 5 times per year, some 4 or 5 times
per month and some 4 or 5 times per week. 400,000 and/or 7 percent is
the correct answer for some combination. Do you define children
between 6 months and 6 years of age? How do we figure the month or two
most chidren skip day care in the summer? There are at least a few
services that might be defined as day care, but their promoters prefer
(sometimes with good reason) to call them something else.  Neil