At some level, I wonder if filing these charges in federal court might not be setting the bait for a ⊥rump trap.
I think the Mueller investigation probably did not go fishing for possible sex crimes, so Nadler’s cooperation at this time might be narrowly constrained to his knowledge of collusion and/or obstruction issues.
If ⊥rump thinks Nadler might have some dirt on him vis a vis crimes related to sexual activity with children, the mumbling about pardons should begin well before the appointed court date.