Hand painted coffee cups

Had the cute idea to let my son paint coffee cups for his grandparents for Christmas. They look adorable but I think I messed up 🫤

I want them to be safe for use & be able to be hand washed without loosing the paint. Is there a way to seal them? I have modpodge (blue label, super gloss brilliant gloss finish) on hand but not sure if that’ll work. I was reading online that I can bake them in the oven at 350 for a while, but not sure if that process will work since we didnt use enamel paint 😭 I don’t want all his hard work to go to waste! Material used was regular acrylic paint and regular ceramic coffee cups from Dollartree. I just hand washed them and he painted them.