Oh, Polly, I am sorry to hear you are going to a funeral.
I think people now-a-days are a little more relaxed about clothing rules than they used to be. I would say that a black skirt and red top would be fine for your girl. Your son would be fine in any church clothes, really, though dark would be preferable. For my boys, I would try for dark dress slacks and a white or blue button down shirt. A collar is a must, but not a tie. Dress shoes would be preferable, but sneakers would be ok if that is what you have.
The main thing, in my opinion, is that you make an effort to show respect to the deceased by wearing clothing that is dressier than usual and not too brightly colored/patterned. The idea is not to detract from the attention paid to the family by calling attention to your clothing ensemble.
Hope that helps and God bless.
Heather