Returned earlier today from a very pleasant trip to Gala Yuzawa.
No snow boots at this time of the year with the 900 gondola/snow fun set - you get a decent pair of wellies (gumboots?), some thick water resistant gloves and a plastic sled. Took rubber boots and gloves for my own kid so didn't need to hire anything else, one sled between us was plenty.
I don't think the snow on the play slope areas was natural, probably from a snow machine. Snow was just like the stuff from a kaki gōri machine (the kind that grinds ice cubes rather than shaves blocks of ice). Made you very wet, very quickly. MissLapLap had a great time, views were spectacular and we went there late purposefully so only caught the good weather today.
We took swimming costumes with us and enjoyed the communal pool areas in the "spa". Highlight was the hot outdoor jacuzzi with a cherry tree next to it in full bloom practically framing the mountain view... Bliss! Indoor onsen was nice and hot, my kid has taken to bathing this way like, well, a duck to water. She was hopping between the cold pool (COLD!) and the hot pool without hesitation, I wasn't the only one surprised at her tolerance for both extremes, she was laughing her head off watching us all flinch. With the locker fees at 100yen (needed somewhere to stash shoes once the rental boots were on), our 5 hours of gondola rides, snow, sledding, pools and onsen came to 1,900yen for the two of us. And we both got our first ride in a double decker Shinkansen. ^