Let's look at that. While I have no problem thinking that this applies to heaven as well, are you saying that there is sex in heaven? How else would there be children? ( I have not expressed an opinion either way here, but am looking at the natural implications of your claims)
Then we have Isa 11 itself, that sets the scene just before the wold and child are mentioned.
Isaiah 11:4
But with righteousness shall he judge the poor, and reprove with equity for the meek of the earth: and he shall smite the earth: with the rod of his mouth, and with the breath of his lips shall he slay the wicked.
That is talking about earth it seems. Now for the icing on the cake..
After we are told of the wolf and child, in the same chapter, we get our bearings.
Isaiah 11:9
They shall not hurt nor destroy in all my holy mountain: for the earth shall be full of the knowledge of the Lord , as the waters cover the sea.
To confirm this yet again in the very same chapter you cite we see this..
Isaiah 11:11
And it shall come to pass in that day, that the Lord shall set his hand again the second time to recover the remnant of his people, which shall be left, from Assyria, and from Egypt, and from Pathros, and from Cush, and from Elam, and from Shinar, and from Hamath, and from the islands of the sea.
So we see there are still nations, and that He at this time recovers the remnant of His people from the various lands some of them still are. This is obviously talking about Jews specifically, and this is obviously on the earth, with nations still here. Your fire idea just went up in smoke.