Stefani's youngest son with ex Gavin Rossdale enjoyed some toothbrush painting with friends, a little music class, and finally a delicious chocolate cupcake, before he and his classmates went after a Captain America piñata.
ET sat down with Rossdale earlier this month, where he opened up about his and Stefani's plans for Apollo's dinosaur-themed birthday party.
"Isn't that weird? Anthropology. Little boys just want dinosaurs! Where do you get that from?" Rossdale mused. "I'm sure he saw a book in his brother's room, but he's crazy for dinosaurs, so we have a party for him and a lot of dinosaurs involved."
"I'm going to have a smaller [party] for him," he revealed, adding that he and Stefani are able to co-parent because of their shared interest in their boys.
"We both have the same interest at heart, their happiness," he said. "It's really simple."