Further, they were quite content to put down uprisings with a rod of iron, so surely a few children being slain in a tiny village (population approx 100?) by a vassal king, would barely even register.
I'm sure the jewish zealots would have taken note of it. Historically we know they were upset with Herod for a number of reasons. Some were probably very legit, others more owing to their overzealousness...They build up a wall so that Herod couldn't see the sacrifices happening in the Temple courtyard from his residence, but as fas as I know they never mention the Matthean account of the murder of the innocents. Neither do the other gospels....Interestingly the parallel fits in with Matthew's portrayal of Jesus as a Moses like liberator. That said, I agree with LT and Kristofer that its likely the Romans cared very little about getting the particulars on every Galilean movement that arose. They'd probably just let it be until it became a nuisance. Then they'd just squash it. I think there was a historical Jesus. Just exactly what he did or who he was is a stumper of a question.