Recently an interview on nintendo.jp has them talking about the development of Yoshi in both SMW as well as Yoshi's Island, and when discussing the aspect of designing the character, they provided this screenshot. Being the huge fan of SMW beta related bullshit that I am I nearly shat my pants when I saw this.
Before you ask, yes, the little slug like creatures are baby Yoshi.
Before you ask, yes, the little slug like creatures are baby Yoshi.