Jollyma-I would just tend to get then to do something simple and age appropriate if they asked for extra homework. This can disappoint some of the parents who want me to to spend my free time photocopying worksheets that they would then like me to mark, but it is far more useful. I would get them to do things like-
Reading-if they asked for extra books, get them to join/use the local library every week and they can read more or the parent can read to the child. This will get the children picking book which will further their interests and also broaden their vocabulary. Parents that want more ORT tree books so that their Connor will be one book of little Tierney don't like this though ;)
Writing-get them to write a diary of what they do at the weekends/during the holidays. They could write stories, letters or book reviews of books they have recently read.
Maths-times tables games, playing with plastic jugs and containers in the bath for capacity practice, telling the time games, snakes and ladders, dominoes, number bonds practice, writing numbers in the sand etc
Helping with cooking, going to museums, playing scrabble-all these things are far more beneficial than a worksheet in my opinion.
How would you, as a parent, feel if I were to suggest these things as a response to asking for more reading/homework?