I'm secondary but I'll have a wild stab... have picture of children's party. How many are people are there? More than 5? Less than 10? more than 100? then I am planning a party at home for nephew or niece how many invites do I need? 20, 200 or 2000? Marbles [or any colourful and countable items] in a jar. Ask the children to estimate and then count them out. Is there enough for one each? That type of thing?