I've been thinking about this for a long time now...

Hazel and Nico probably never found out that Santa doesn't... you know...

The Argo II gang plus Reyna, Thalia (who were visiting Camp with the rest of the Hunters) and Will and made sure that no one ruined that for them.

When the two children of Hades fell asleep, the gang placed the gifts under the Hades Cabin Christmas tree.

Leo and Percy ate the cookies and milk because "free midnight snacks".

Jason and Frank slipped at least five times during this process. One time, Jason hit his head on the wall and got a huge bump on his head.

Nico woke up once due to the commotion but fell back asleep realising it was probably Santa. He even heard a vague "HO HO HO!" at some point, confirming his thoughts, which was basically Percy and Piper having fun outside while Annabeth and Reyna tried to shush them.

When they were finally done, they were all dragged outside by an exasperated Annabeth.

But it was all worth it, judging from Hazel and Nico's exhilarated expressions when they received their gifts the following morning.