You need to have @OneToMany(..., mappedBy = "parent"), otherwise you will have 2 associations that are not bidirectional that use the same foreign key, which is not supported.

JPA 2.1, Section 3.4.2 Version Attributes says:

"All non-relationship fields and properties and all relationships owned by the entity are included in version checks"

Section 2.10.2, Bidirectional ManyToOne / OneToMany Relationships says:

"Assuming that:

Entity A references a single instance of Entity B.
Entity B references a collection of Entity A [21]
.
Entity A must be the owner of the relationship."

If you want to include the collection in optimistic locking checks, then @OptimisticLock(excluded = false) is the way to go.