Woodwaj nit sure if anybidy has suggested it and i can't fibf your post now but in the past I've done the pound footballs very successfully as party gifts - along with a slice of cake or sweets. Asda and poundland have them; often with non-foitball designs on if there are girls/boys that hate footie going. Woukd recommend taking a sharpie so you can name them as you hand them out so they dont get muddled (at the party or at school afterwards if dc can take them in)
Poundland usually have hotwheels cars for a pound too which can be a nice gift if the age group is right.
If you want to put several bits in, sports direct do tennis balls which have gone down well for about 30p, I've supplemented with some bubbles from poundland (box of 9 for a pound) and notebooks from poundland (several in a pack) that had blank covers that ds decorated for each person.