Narcissa, I made my comment, wondering if the OP is trying to avoid conspicuous consumption.....one element of this could be seen as children getti g heaps and heaps of presents. Another aspect of it could be seen as having very large parties for huge numbers of children involving lots of expense, food, party bags etc.
Personally I am not especially against either. Was trying to understand the OPs motivation behind saying no presents and give to charity instead.
If children are very little, I agree that you might want a big party, so no one is left out. However this does not have to be 'big' in terms of expense. I know people who have had whole class parties in a Church hall, costing £15 to hire for 2 hours. They don't have an entertainer, but do lots of games and give a sweet as the prize, very very simple party food and a party bag which probably costs 50p. They can have hoarders of children and they all seem to have a great time. I think the OP meant large in terms of numbers and expense.
I think a lot if people find giving to a charity not of their choice, instead of giving a gift uncomfortable, whether it is for adults or children. As someone said, they prefer to give to a charity of their own choice. It can also make people fee under pressure to give more than they may spend on a gift (I know the OP clearly said she takes no notice of how much anyone gives or does not give...but I still feel it makes some people feel awkward)
If the OP doesn't want gifts for child, I think it would be better to say so and not bring charity into it. Should be aware though, of this also making people feel uncomfortable about attending without giving a gift....people feel they are contributing/covering the cost of their child that way....might not be correct, but people feel like it.
Final thing, I think it is important to make guests feel comfortable. I'm sure the small children attending dont bother about it all one way or another, but the parents do and adults do in situations when they are invited to parties. If the OP is keen for charity to benefit, perhaps she should consider making a donation herself, as part of her party planning expense.
Once children reach about 6 or 7 I have found the large parties (in terms of numbers) significantly reduce, so this issue is fairly short lived anyway. Once only 5 or 6 are coming, can't see any prob in receiving. Few presents. OP can give to charity if she is keen. Not sure it is helpful to make others feel they must.