do my baby need A car seat to ride amtrak train?
Yes, he do.
It depends how old your kid is. if he is above 2 years old, he can just sit on your lap. If he is a year and younger, he should be carried in a portable stroller or any type of movable seat or car seat.
Normally its optional for you you should asked where you purchases you ticket at would be okay to hae a car seat for your child or just bring one on your own.