Personally, I don’t think animals are going to be with us in heaven. Romans 8 says that all creation has sinned and that includes animals too, so all deserve to die. The life we have in Jesus is based on our belief and faith in Him – animals don’t have that. Besides, God wants us with Him, not animals. There are no verses in the Bible that I know of that say clearly that animals go or do not go to heaven, but many people think they don’t. And
I think they’re right.
We would love to have our pets in heaven, but if God does that how would a spider or a worm feel? You wouldn’t want those in heaven, would you? But they’re God’s creation too… And besides, do you think that once we see God and begin to explore His character and being we will still be fascinated by our pets?
And about the verses posted above… Isaiah 11:6-9 speaks about an earthly kingdom of God, not heaven as described in the NT. During that time the Earth and its creation will probably be restored to its former state, so will the animals. Ecclesiastes 3:18-21 doesn’t speak about man or beast going to heaven; more like the process of returning to earth, the process of putrefaction. Both man and beast (their bodies) have the same end.