You are just bullshitting. By your accounting, if your employee quits, or falls ill for a month or two, which would have the same impact as the training period for the maternal leave replacement, your kids would not be able to afford college [1]?

Does your employee Ski? Because ACL tears are damn common, and medical leave for an ACL tear is up to 3 months.

[1] (which if you're really not in the US should be free anyway)