they were only 4 months old ... one male and one female ....
Haha! Opus I was just reading the same link as you! With rabies they would exhibit more neurological symtoms. I don't think that's what happened. Feline parvo could be possibility. How old were the kittens? Do you know?
I'm not real familiar with rabies...but when reading the symptoms on the following site it doesn't really sound like death would be that quick, the kittens would have shown major behavioral signs before...
http://www.petmd.com/cat/conditions/neurological/c_ct_rabies#.UgROr21hMbA
What about rabies does the above symptoms correlate to that???
I agree with above. They could have ingested something. They also could have had worms or fleas and been anemic. There are soo many things that could have happened. Its hard to speculate. Know this what you did was very kind and loving. Find some peace in knowing that
((hugs))
With them being outside unsupervised, it could be anything. Sounds like the may have ingested something poisonous like antifreeze.