Child going on holiday with grand parent

What’s the procedure for this? My mum wants to take my daughter on holiday for less than a week and my daughter is excited! I do agree that the holiday would be good for the both of them… does anyone know what the procedure is in terms of consent? Do I just write a letter?

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To add more context: we live in the United Kingdom and my mum has her birthday holiday planned in which she would like to take my daughter with her. The holiday is to Turkey.