Dad, it depends on the state, but in general if your "extra" jobs are a permanent feature of your life, they are viewed as part of your income. If you're working overtime now and then, or you take an extra job to make ends meet during some emergency, that's a different matter.
The other thing is an LLC can generate significant income that doesn't stem from your own work. If you have employees and they're busting humps for you, and you're taking home $60K profit each year, then yep, that's part of your income. Your children are entitled to a slice of it.
Which also means, OP, that your lawyer needs a look at the financials for the LLC. Hire a good lawyer and an accountant to go over the records and returns. If he's hiding money this is also a matter for IRS.
SRS, if your ex is in arrears, will your state support-collection agency enforce and intercept the money?