MC-3776 (IPv6 Does Not Work) is marked as fixed, so I went to test out Minecraft between two IPv6-only hosts. While it is possible to connect to another multiplayer session over IPv6 by entering the IPv6 address manually in the "server address" box of the "direct connect" UI screen (you have to remember to enclose the IPv6 address in square brackets so the port number can be distinguished from the IP address segments delimited by colons (what are these called? IPv4 called the octets, since they were 8bits. So hexidectets for IPv6? Ed: sources suggest "hextet", "hexadectet", "hexadecatet", "quibble", "quartet", or "piece")).
But IPv4 multiplayer servers on your LAN show up automatically under your list of multiplayer servers, so the kids can connect without manually entering IP addresses. This functionality should also work with IPv6.
Note that while it is possible to play multiplayer over IPv6, you still have to be dual stack, because IPv4 is required to download the jar files (
MCL-2627 Launcher will not download game over IPv6) and to authenticate to Mojang
This may be a manifestation or consequence of MC-98598 "LAN List does not populate reliably"