How much water does a plant need daily? What do plants eat? How much sun does a plant need daily? Is there a certain type of soil a plant needs? How many plants are in Indiana?
Light (sun) requirements generally depend on the type of plant grown, as some varieties can thrive in little to no sun. As for the number of plants in Indiana---there is no surefire way to get an exact number but I'm guessing it would have to be in the thousands.
You have many questions and while I cannot answer them all, here are some articles that you may find helpful: https://www.gardeningknowhow.com/houseplants/hpgen/how-to-water-a-plant.htm
https://www.gardeningknowhow.com/edible/vegetables/vgen/fertilizer-options-for-your-vegetable-garden.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/what-is-soil-made-of-creating-a-good-garden-planting-soil-type.htm
We need to know how much water and sun a plant needs every month.
It depends on the plant. What kind of plant are you caring for?
Seeds are formed after fertilization. What happens during fertilization?
This article should help you understand more about how the life cycle of plants works: https://www.gardeningknowhow.com/special/children/basic-plant-life-cycle-and-the-life-cycle-of-a-flowering-plant.htm
Can humans do some pollination?
Yes, in certain instances when needed, hand pollination can be done. This is most common with tomatoes and squash but is similar with most other plants as well. These articles should help: https://www.gardeningknowhow.com/edible/vegetables/tomato/pollinate-tomatoes.htm
https://www.gardeningknowhow.com/edible/vegetables/squash/pollinate-squash-by-hand.htm
What is a soilless planting? Does it mean like small gravel?
There's no real soil in soilless mixes. Most brands contain peat moss, vermiculite and perlite. Other additions include composted bark and other organic materials. Soilless mix is lightweight, water retentive, and well drained. Here is more info: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/soilless-growing-mediums.htm
If many annuals can self-seed, why are they still considered annuals?
Can you give me some ideas for a project for kids 7-12 yrs old? This 'workshop' will be 1-2 hrs long, 6-12 kids inside a greenhouse on tables. I need to use fairly inexpensive materials. Have available all kinds of plants-greenhouse and nursery. Past projects have included: moss garden, herbs, built a birdhouse.
You could try a "grocery store garden". You can pot up things like pineapple tops, avocado seeds, potatoes, sweet potatoes and carrot tops, which will all grow for them. Here is information on these:
https://www.gardeningknowhow.com/special/children/planting-pineapple-tops.htm
https://www.gardeningknowhow.com/special/children/sprouting-avocado-pits-how-to-root-an-avocado-seed.htm
https://www.gardeningknowhow.com/edible/vegetables/sweet-potato/grow-sweet-potato-plant.htm
https://www.gardeningknowhow.com/edible/vegetables/potato/how-to-grow-potatoes-when-to-plant-potatoes.htm
http://www.weekendgardener.net/blog/2007/09/grow-carrot-top.htm
I don't know if you have enough time for this one, but you could do a potato bonsai. You chit the potatoes (chitting is what happens when a potato sprouts before planted) and then the kids can trim them like bonsai trees:
https://www.gardeningknowhow.com/edible/vegetables/potato/sprouting-seed-potatoes.htm
You might also build a mason bee house (to attract pollinators to the garden) or a bird nester (which provides materials for birds to build their nests): http://www.nwf.org/Get-Outside/Outdoor-Activities/Garden-for-Wildlife/Gardening-Tips/Build-a-Bee-House.aspx?CFID=28625570&CFTOKEN=64ada46852abd4d-4CFC037F-5056-A868-A085CD4C912568A8