I know there are cultural differences at work so it may not be the same in Australia (or the US) - but here back home it's customary for the family to express where donations may be made in order to honour the interests or wishes of the deceased. (Oh God, that horrible word!) 
If that's the same in Australia, then surely the Ledger family may be expected to say something along those lines very soon, especially since they know there are many people around the world who grieve and would like to honour Heath in some way.
Not that I don't think both AIDS research and childrens' charities are entirely deserving of donations, of course, if the family decides not to say anything specific about this topic.
It's an individual thing here in Australia, Mikaela. There are no set rules, per se.
In Australia, if there are any specific considerations, they are usually stated in the formal funeral noticed, placed in the press on the family's behalf, by the funeral directors (undertakers).
So the general rule is that if the funeral notice simply states the date and time of the funeral, it is OK to send flowers to the designated location at the appointed time.
However, if flowers are not wanted, in the funeral notice it will state something like, "Please no flowers," or "Donations to the children's ward at ........ Hospital in lieu of flowers please."
Most people here in Australia wait to read the funeral notice before they make their tribute arrangements.
I'm sure that flowers are sometimes sent to a funeral, even after a family requests that none be sent. On those occasions, it is my understanding that the funeral directors redirect them to a local hospital, for distribution on the wards.
