* As a plural noun: kids' sandwiches (The apostrophe after "kids" indicates possession.)
* As a modifier: kids sandwiches (No apostrophe is needed since it's not showing possession.)
Example:
* "We made some kids' sandwiches for the picnic." (The sandwiches belong to the kids.)
* "The menu had a special section for kids sandwiches." (The sandwiches are for kids.)