"He's a very responsible little boy. I'm more likely to hurt myself than he is!" Still, now he was worried. He entered the house, made sure that the wards on it would let Remus pass as well and then he called out immediately, looking around. "Harry?! I'm back!"

He hadn't been worried until just now, but suddenly he was filled with worry. "Harry? I brought your nanny!"

Well. He was filled with worry, not with an inability to crack a joke.