Why am I not getting a prompt to enter 529 contributions in the State return section? Or where do I enter 529 contributions?

The 529 contributions are entered on your Michigan return.  After you enter your residency information, your county, school district, and what cities you need to file, you will get to the Here's the income that Michigan handles differently screen. Select to enter your Contributions to Michigan Educations Savings Program.

Do I need to put my contributions to 529 for minor children on the michigan state income tax return.  These are contributions that are made after taxes

Yes if they are MI 529. MI will reduce your taxable income.  "Michigan taxpayers may also be eligible for a Michigan income tax deduction on contributions made to MESP up to $10,000 for married couples filing jointly or $5,000 for individuals filing single per year. A Michigan taxpayer is permitted a deduction from Michigan adjusted gross income for a contribution to an account less any Qualified Withdrawals made during the tax year." from MESP

@Marchet