Where are James, Lily and Snape during the Fantastic Beasts movies? Are they at Hogwarts or are they still too young to be at Hogwarts?
They weren't even born yet
Fantastic Beasts and Where to Find Them takes place in 1926 and Fantastic Beasts: The Crimes of Grindelwald takes place in the following year, 1927.
EXT. SOMEWHERE IN EUROPE—1926—NIGHT
Fantastic Beasts and Where to Find Them - The Original Screenplay
EXT. NEW YORK, AMERICAN MINISTRY OF MAGIC—1927—NIGHT
Fantastic Beasts: The Crimes of Grindelwald - The Original Screenplay
On the contrary Lily, Snape and James were all born in 1960, a lot later than the Fantastic Beasts films we've seen so far.
The headstone was only two rows behind Kendra and Ariana’s. It was made of white marble, just like Dumbledore’s tomb, and this made it easy to read, as it seemed to shine in the dark. Harry did not need to kneel or even approach very close to it to make out the words engraved upon it.
JAMES POTTER LILY POTTER BORN 27 MARCH 1960 BORN 30 JANUARY 1960 DIED 31 OCTOBER 1981 DIED 31 OCTOBER 1981 The last enemy that shall be destroyed is death.
Their births are even the same going by film canon.
That doesn't mean we won't see them though as we know these films are already playing fast and loose with the timeline. For example, they changed Minerva McGonagall's birthday/age.
The first Fantastic Beasts movie was set in 1926. The Crimes of Grindelwald was set in 1927.
The dates above come from Pottermore, however, since Pottermore no longer exists, the Pottermore Wiki links are the best I could source for the birthdays.