The airport was ranked the top in a new study.
It was praised for its dedicated children zones and breastfeeding facilities.
The research also looked at the average price for a child at the airport lounge and at which age children get free fast track.
At £20.53 per child, it was not one of the cheapest lounges, but the other factors helped it gain its top spot.
In second place was Luton airport, which offers much of the same features but its lounge is more expensive, at an average of £21.49 per child.
The study, by Paying Too Much, a holiday and travel insurance comparison site, also found the least family-friendly airport.
A spokesman for Paying Too Much said: “With specific breastfeeding facilities and play areas available onsite, Gatwick airport is well-equipped for families with young children.
“Cardiff is the least family-friendly airport, with no breastfeeding facilities or specific areas for children. For families wanting to book into a lounge, it also sees the highest prices for children, costing the same (£32.99) for both adults and children.”