Actually there are many cases of kids having different recollections as kids than adults and considering Mia Farrow's documented history of child abuse to her own kids (2 of her kids committed suicide, 2 spoke of abuse, 1 died penniless on the streets), it's extremely realistic.

The train story also has been discredited and was never recalled in any of the two independent investigations in 1992:

https://ronanfarrowletter.wordpress.com/2021/02/28/farrow-v-farrow-the-case-of-the-magical-disappearing-electric-toy-train/