USA Hockey applied the NHL’s cutting-edge analytics technology to eight-and-under players, and found that the kids played more like the pros when they played cross-ice, rather than on the whole, wide-open rink:
Smaller rinks came up while discussing kid-sized spaces earlier.
As a former kid, a pretty good rule of thumb (on frozen lakes) is that kids don’t need any more ice than they can keep shoveled. I’ll bet it’s close to NHL rink width in length, and maybe 20 feet wide.