My name is ***** ***** I am an experienced criminal
No, they don't have to give you the warrant in order for it to be valid. It's enough that they have one. And yes, if what they find during the search gives them probable cause
for an arrest, they can remove people from the household.
They can take all electronic devices and obtain a further warrant to search their contents. What does not contain contraband will be returned to him eventually. What does would be held as evidence to be used against him once charges are pressed.
Although your son has not been arrested, the Federal government is involved in this case, which may mean a federal rather than a state prosecution, depending on what they find. The resulting charges are potentially very serious, even for a first arrest. There is nothing right now for a lawyer to do, but it's a good time for your son to start consulting with local criminal lawyers with experience in both state and Federal court
, so that in the worst case scenario he has someone whom he trusts who's already been briefed on the issue and who can step right in to represent him and safeguard his rights.
Until he has counsel, he should not be discussing this incident with anyone, since anything he says about downloading child porn to anyone other than his lawyer could be used against him. If the authorities want to question him, he should tell them that he wants to hear from his lawyer first before answering any questions. He has no obligation to cooperate with the authorities and give evidence against himself. In fact he has a Constitutional right that allows him to avoid self-incrimination. The only way he should talk to the authorities is through or with a lawyer.