They shouldn't be attacking them piggies, might happen to chickens and wolf cubs too but haven't tested it.
Edit: As a temporary workaround I tried changing the piglet to use the Players faction instead, by using FactionAssigner and it fixed the issue. Here's a list of all tameable infants:
- Asksvin_hatchling
- Boar_piggy
- Chicken
- Lox_Calf
- Wolf_cub
They shouldn't be attacking them piggies, might happen to chickens and wolf cubs too but haven't tested it.
Edit: As a temporary workaround I tried changing the piglet to use the Players faction instead, by using FactionAssigner and it fixed the issue. Here's a list of all tameable infants: