J.W.
Yes and no, some tissue and some organ donations can be done. There are some organs that cannot be donated to a child or the other way around. I don't know that list. It is one of the reasons the donor list is so long for children, you not only have to match blood type and all that but age has to be close as well.
Unless you luck into finding someone here that has been through all this I would suggest asking your doctor.
_____________________________________
Looking at your what happened, you cannot set the time frame. Organs are only viable for a very set amount of time. As awful as this sounds they will keep a donor on life support to keep the organs viable until the recipients are there and then they harvest.