You're not making a fool of yourself, Faithful, you are simply looking for answers from your sister. Accepting one package and refusing another is a little confusing for the sender. Your email was simply conveying that, without being mean or rude. You sent your love. Now perhaps it is time to let it go for this year if she doesn't respond.
Next year perhaps you can send the packages the day after Christmas, so the children still receive something, like normal kids, but I think they might accept them if it's AFTER the holiday. Worth a try for the kid's sake. Keep being the good hearted person you obviously are. You are setting a great example not only for your own children, but hers as well. And for others who are aware of this situation. All the best to you.