What are the custody rights & initial legal actions 4 parent who's been left?

[cybersleuth]

Hello,
I'm a multi-year resident of Illinois, in the same house as my spouse and three children ages 13, 12, & 10.
My spouse took our three children yesterday, intentionally sneaking away, and a communication blackout.
I know where they are, 200 miles away, in an otherwise safe environment, but still in Illinois.
Sufficient personal effects are gone to imply that the spouse has moved out with the children.
No illegal or other negative provocation or conflict has occurred.

What legal steps can I take, to ensure I maintain the ability to have my children "back".
No legal action is known to be in effect or have been taken by either spouse to date.

Thank you, again my question with the context is, "What are the right steps to take, to get my children 'back'"; knowing that forcing a conflict between spouses doesn't fall within the scope of an answer.

Thank you, sincerely

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