Rather than buying an actual voucher and risking the airlines various restrictions, or the chances that they'll change their policies mid-year and thus causing you hassle, would you not just put an IOU note in an envelope and let her know that you'll send her and the child away during the year. It may not be the most romantic, if that's what you're after, but I'm not convinced about the merits of airline vouchers.
They don't seem to have any restrictions. I received one as a birthday present and was able to part use it and then use the balance to part pay another flight.
A big advantage I noticed was that if paying with a voucher you avoid the credit card charge.
One thing to remember with the Aer Lingus vouchers - you must buy them in the same currency as the origin of the flight. e.g if you're in Ireland buying a voucher to get your daughter home from London, buy the voucher in GBP, not EUR.
For Ryanair or Aer Lingus thinking of getting vouchers for xmas. If the flight comes to €140 and the voucher is for €140 do they allow you to use the €10 on another flight.
Callybags- I see you said its possible but I remember someone tell me they could not. How does it work do you get a new voucher with the balance?
Anyone got them for Ryanair and use voucher to pay for full flight and then usd balance on another?