Don't dispair! There are many options available. You might want to create a garden around an existing walk-way. This can be done easily by planting in layers. You need about 12" of depth for each layer of plants. For instance if you want to plant 2 rows of plants you would need 12" of depth. 3 rows of plants will need 24" of depth, etc.
When you have decided how many rows of plants you will plant, you need to choose plants of varying heights to fill each row, For instance you will want to put tall plants in your back row, medium height plants in the middle area and short, border plants in your front row.
This type of walk-way garden is great for city gardens or school gardens with well-established walk-ways. Kids may plant single rows of plants around their driveways or sidewalks at home, but keep in mind that the butterflies don't always visit noisy or busy places. A window box garden might be better if there is a deck or backyard area a child may plant in. The box will keep things localized and will be easy to view during summer holidays.