Oh dear - this is well above my level.I haven't done it myself personally, but I remember watching my mom decorate cakes when she had a cake decorating business. I included a video that shows how to use the grass tip with buttercream icing.
I am looking forward to seeing everyone's dessert that they are making!
I was thinking of making some brown blob shaped biscuits and putting a mouth, eyes and nose on them.
I haven't ruled out using a Sharpie if necessary, because surely they aren't that toxic, and the kids have eaten way worse things in their time