Here is an updated version of your description that fits under the 700-character limit and incorporates homework help, preparing snacks, and meal prep:

We’re looking for a babysitter to help with our three elementary-aged children starting September 21st (start date is flexible).

Duties include supervising the kids, engaging them in activities, helping with homework, preparing snacks, and handling light meal prep.

The sitter needs to have a car and be comfortable with pets, as we have a medium-sized miniature pinscher. This position is ideal for someone who enjoys being active, keeps safety a priority, and loves working with kids!