Print your tax return and mail it in. When the IRS gets around processing it, they will pay your refund based on you claiming the dependent. Then, they will send letters to both sets of parents to start an investigation and you will have to send the IRS proof that the child was your dependent.
Because the IRS is not processing paper tax returns at this time, if you are expecting a large refund, your other option would be to remove the child as a dependent and file the rest of your return electronically. Then, when things get back to normal, you can file an amended tax return it to add your dependent. After the amended return is processed, the IRS will start the same investigation of the dependent claim.
Because of the delays this year due to the coronavirus, I think there are going to be a lot of back logs at the IRS. If you can afford to wait on your refund, I still think it would be better to mail one original return with the dependent, instead of e-filing a partial return and then filing an amended return later.
