Any riskier than covering a younger person having children? I had a friend who's wife had a premature birth with complications. Thirty days later, a bunch of it in neo-natal intensive care, I'd bet the hospital bill was pushing a quarter mil. So by your logic companies shouldn't cover younger employees families either.
Small companies who provide health insurance for their employees will bend over backwards to hire young single people or people who have government employees (who have much better family health benefits than the private sector) as spouses.
Count the beans.
Funny but where I work it is the younger employees who are always calling in "sick". The older people have a better attendance record.
One young woman programmer was hired at the place I work at. She was 6 months pregnant when hired. After 2 months, mostly spent in learning how things worked, she goes on maternity leave for 6 months (with benefits). She returns, is immediately pregnant again, goes on maternity leave again. Then quits to spend time with her kids once maternity leave is up. She essentially milked the system