The under sixes are one of the easiest age groups to entertain as really all they crave for is attention from an adult!!
...in the age of television games machines and mealtimes on laps many children today are starved of quality time with their parents and sitting in the car, train, plane together is one of the only times they are all togather without distractions. There are many FREE games on this site to entertain little ones 'I SPY' was recently voted one of the most popular games for families on the move (probably because you can involve the whole family and temper the question to suit the age of the children).
Variety is the key to a happy journey and half an hour is just about the maximum attention span on 1 topic so once you have exhausted the free games you might like to think of other ways to entertain them.
Make sure they have a flat surface to play on (this site stocks some fantastic soft travel trays specially designed for little ones) and have some finger food at the ready to separate each activity. Snacks such as breadsticks, carrot battons, raisins, cheese sticks and pieces of fruit such as grapes, berries, slices of apple (oranges are dreadful because the juice gets everywhere) are good choices nothing too rich and not chocolate, which melts everywhere and makes a huge mess.
A bag of colouring pens, books, Duplo, toy cars, and picture books are essential, and include a few new things to keep kids interested for longer. Maybe make up a goody bag for them with a few new toys and activities.
Travel sickness affects many children. There are over-the-counter or herbal medicines you can use, and many people swear by acu-pressure bands, available in chemists or online. Car games that involve looking out of the window can also help, as does fresh air.
Listen to some music or stories, maybe buy some finger puppets and act out the songs and stories on the CD's. Buy them some colouring books, activity books and, as long as they dont get travel sick, let them colour, play noughts and crosses. Chat about the journey, play some more games ... let them have a sleep (if you're really lucky!!) its amazing how quickly a 3 hour journey will go seperated up into half hour slots !!!