Loved this film as a child and still do, but watching it as an adult I realised the parents were very selfish.
They each hid the fact their child had a twin and allowed other close family members to also hide this fact.
They let each child believe that one had a mother and one had a father that was never interested in being in their lives.
The mother even said they had the arrangement so she’d never have to see the father again ... and therefore never being that bothered about even seeing how her child was doing/growing up
And I never saw them ever apologise for their actions. It was actually the twins worried their parents would be angry at them for switching.