When i had my children we opened trust funds with the children's mutual they sent me a link to another project they run call child trust fund cash back in which you or your children's trust fund make money through spending on-line via their website i have used it for shopping at mothercare and asda!!
i had a look and there are lots of different travel companies Thomas cook, beach collections etc. its free to join and you can earn up to 5% on some sites and by booking your whole group together you may make enough back to pay for other things!!
its what im hoping to do so just thought id share!!
hope its of some help