My husband and I left our 8 month old daughter with family while we went on our honeymoon to Mauritius. It was a 6 hour flight to Dubai, 2 hours at airport, then another 6 hours to Mauritius. It would have been far too hot for her, unfair to take her on the flight, and too difficult to sterilise bottles etc etc.
We went for 10 days so my husband's mum had her for the 1st 5 days and my mum for the other 5. We missed her like mad but a couple of days before we came home, found out she's had an awful sickness bug. It was horrible cause we just wanted to get home to see her, so we paid £250 just to go home a day early.
Don't think I'd leave her again BUT it was our honeymoon and too far away.
My sister-in-law is planning to leave her baby in May (he'll be 3 months old then) with her mum for a week while they take their 2 year old daughter abroad. They really want a holiday, know their son will be in safe hands and don't want their daughter to miss out.