Allow employees to work four 10 hour days per week, the other day, they act as a cooperative child care provider. Each employee can drop their child off at a provided day care center 4 days per week. The 5th day they provide 10 hours of child care for their own child and the other Federal Employees children in the program. The "day off" of work may be Tuesday for one employee and Thursday for another, and that extra day the employee works 10 hours as a child care provider. The other 4 days, the child care is basically free, as the other Fed employees will be looking after their child at no additional cost to them.
This would be a 100% voluntary program. (I can't believe I actually had to put this in)