# Factory bot pass other params to create other objects
FactoryBot.define do
  factory :example do

    transient do
      children []
    end

    after(:create) do |example, evaluator|
      evaluator.children.each do |child|
        # do what ever you want
        create(:example_to_child, example: example, child: child)
      end
    end
  end
end

create(:example, children: [create(:child), create(:child)])