So, what I'm hearing is that you have $16,800/yr in cash savings PLUS your husband is putting or will be putting between $10,000-$13,000 of his admin salary into his 401k for a grand savings total of ~$27,000/yr.
Here's a compound interest calculator for you:
http://www.moneychimp.com/calculator/compound_interest_calculator.htmEarly retirement is not an impossibility. I'm guessing 10 years, maybe 15 for your husband. Here's why: in 10-15 years, you'll have fewer kids in the house, and those that are left will be old enough for you to work full time. Meanwhile, your husband will have received raises, maybe he will even switch jobs to a more lucrative employer. Your expenses will be going down while you and your husband's incomes are growing.
Although, you both might be able to retire sooner if you're not starting from zero. How much do you have in assets currently? Is your house paid off?
Try to get your expenses lower now by looking around on this site for ideas. Maybe you want to do a case study where Mustachians weigh in on where you can optimize.