When filing a return do I need to provide proof the child stayed with me for more then fifty percent of the time ?
Or will I need that only if they look into that ?

you JUST need to Keep detailed records of receipts and documents to show proof of the support. You do not need to submit ?em to IRS/your home sate Having an organized filing system will help you stay up to date so you can easily provide the necessary information to the IRS. In fact, keep your records on file for several years, just in case the IRS conducts an audit of your tax records.
Or will I need that only if they look into that ?===>Yes as you said.