It is worth thinking about the setting too. Games with a drawstring bag or a tin survive being thrown in a rucksack better than a large flat box. For a caravan or a beach hut with limited space, pick a few small games rather than one big one, so you can match the game to the mood without taking up a whole shelf.
By eight to twelve, most children enjoy games with a little strategy or a competitive edge. Word and number games, such as WordSnap XL, and family favourites like Snakes and Ladders in its bigger 3D versions give them something to plan around and enjoy together. Mixed-age families get on best with games that scale, so older and younger siblings can play the same round.
Slower, more thoughtful word games suit older children and adults who like to plan a high-scoring play. These reward a wider vocabulary and a bit of tactics, so they are better kept for players who enjoy taking their time. If you are buying for a mixed-age family, a fast game is usually the safer bet, since it keeps the youngest involved rather than left behind.
Difficulty is worth checking before you buy. A puzzle that is too easy gets solved once and put away, while one that is far too hard can end up back in the box. Many puzzles carry a difficulty rating, and it helps to match that to how much time the person likes to spend. Someone who wants a ten-minute coffee-break challenge needs something different from a person happy to pick away at the same puzzle over several evenings.
To compare word games by pace and age suitability, and see which reward speed versus vocabulary, take a look at the word games at educational brain games for adults for kids.
Solo puzzle games are useful when you need to keep one child occupied without a second player. The Genius Square and Genius Star are self-contained, so a child can roll, place and solve on a tray table or a picnic blanket without anyone else joining in. Card games such as Flip 7, available from The Happy Puzzle Company, come into their own when the whole family wants a quick round at a campsite or in a holiday cottage.