One of our children went on holiday with friends. We gave them her E11 card and our vhi details. We also typed up a letter stating that in the event of a medical emergency, they had permission from us to get the relevant treatment. Thankfully, the forms weren't needed. Naturally she had her own passport and we had her well versed in what not to carry on a flight etc. Other than that, we told her to make herself useful and to move out of earshot in the event of a family disagreement!!! She had a great time.