Need to 'borrow' miles from your kid to get that free flight? A big airline will let you do that

Don't have enough airline miles for that free flight? United Airlines is now letting people pool and share their frequent-flyer points with family and friends, a feature currently offered by some smaller carriers.

United said Thursday that a “pool leader” can pick up to four other people to set up a joint account in its MileagePlus program.

The group leader must be over 18, but there is no minimum age for others, so parents can sign up kids. Everyone in the pool must have their own United frequent-flyer account.

JetBlue Airways, Spirit Airlines and Frontier Airlines already offer pooling, with the rules varying a bit from one to another.

Frequent-flyer programs remain popular despite complaints that the value of miles and points decline over time because airlines raise the requirements for redeeming them for flights or other items.

The programs are valuable to the airlines by increasing customer loyalty and giving consumers a reason to get an airline-branded credit card. United’s credit cards are issued by Chase.

United points are in the middle of the pack for value among programs at U.S. and international airlines, according to a recent analysis by the consumer site NerdWallet.