I am a US citizen married to a UK citizen. We have been living in the UK for 6 years and my children were born here. My one daughter has her US and UK passports but my other daughter has neither yet. We are planning to move to the US soon and I know they both need their US passports to enter the US but my main question is does she also need her UK one to leave the UK? We don't want to get both now if we don't have to.