This is going to sound really odd, but i've been trying to create a sort of cover-up dress, one of those simple tunicky things, but for toddlers/ children. The thing is, i think it will be easier just to lengthen a t-shirt rather than seriously edit a dress mesh. So my question is, i presume that i need to asign bones to it, but how do you exactly go about such a thing? good luck understanding this

For children i still would use a dress and cut the bottom/legs off.
Toddlers will be a bit harder i guess cos there isn't really a mesh available.