A Wand of Wonder I gave them early on has provided my party with some hysterical moments.

Yes, that’s my understanding as well and how I’ve ruled in my game

Gotta be this

Bears, wolves/direwolves, giant eagles, hell the druid in the game I run summoned an auroch and rode it into combat once. I limit it to beasts the player has encountered personally or would reasonably know enough about their anatomy to summon, and then just limit what I expose them to.

As far as preventing cheesing with 8x small beasts and turning the battlefield into chaos? I recommend enemies with AOE attacks to clear the field.