Terrariums can be as simple as a single plant in a recycled jar. A container with a lid will help retain moisture and cut down on the need for watering, and the soil should supply all of the nutrients the plants need.
A terrarium can also be home to snails or frogs. If lizards aren't your cup of tea, use plastic "pets" instead. Be sure to do your research before introducing an actual animal into a terrarium.
If this is your first terrarium, start simple. Select a container (with or without a lid) that can accommodate all of the materials. Good options include fish bowls, cookie jars or large vases. Generally, the container should be deep with an opening wide enough so your child can easily slide his hands in and out to work with the materials.
Next, choose your plants. Buy an assortment of succulents or small woodland plants from your local garden shop or a home improvement store. Select plants with similar growing requirements. If you're feeling ambitious, plan a nature walk through your local forest preserve to collect moss, small stones or other material.
An odd number of plants usually looks best, so choose either three or five plants. Choose plants in a variety of heights and textures to create visual interest. Consider adding at least one plant that flowers.
Place a layer of gravel or rocks on the bottom of the container to allow for drainage. Pour a layer of potting soil mixture over the rocks. The rocks and soil together should take up about one-quarter to one-third of your container. Remove the plants from their containers, loosen the root ball and place the plants into the soil. Place interesting stones or mosses around the main plants.
A few inexpensive embellishments will really make this project fun and whimsical for the kids. Add accent pieces such as miniature plastic dinosaurs, bugs or lizards. Suddenly, a few plants and some soil have been transformed into a Jurassic wonderland.
When all of the pieces are in place, water the terrarium and replace the lid if you are using one.