www.printroom.com
$99 a year plus a small percentage of whatever you charge for prints. It's geared for exactly this sort of thing. You get to spend your time shooting... Rather than maintaining a big website, collecting payments (including sales taxes, which you need to send to local/state gov't regularly), dealing with credit cards (which costs a lot of money to do), making quality prints, packaging and shipping them out.
I leave all the money collecting and order fulfillment up to Printroom!
Plus through them I can offer my customers around 65 sizes and finishes of photos (which is actually only about 2/3 of what they offer) as well as a selection of about 25 other items like key chains, coffee mugs, coasters, puzzles, calendars, etc.
To offer this many choices at home would mean a huge investment in supplies and equipment, not to mention learning how to use it all quickly and efficiently!
You'll still need to edit your shots, organize them and upload thumbnails. Printroom provides software that handles creating the thumbnails and uploading them, and manages your galleries online, as well as your images on your computer.
A couple years ago we used SmugMug and the prints weren't good. I have heard from folks recently that they are much improved, though.
There are more features to Printroom, such as means of tracking traffic to your site, but the above are the most important, I think.
There are other companies that offer similar services to Printroom, some of which seem quite good and might do as well.
Get a good, fast workflow and backup in place, ASAP.
For each venue where you might shoot, find out who is the organizing authority, get with them to find out if they have any agreement in place with another commercial photographer already. If so, you can't shoot there and sell the images. If not, sign a contract with them as the exclusive commercial shooter of their events for a year (or whatever). I will not photograph events where I'm not given the exclusive, period. It's just not worth it! In exchange, allow the organizer to use some your photos as a way of saying thanks, and position your online galleries as a convenience for their participants and attendees to browse, with picture purchases optional.
Regarding your concerns about putting the photos out online for anyone to see, this is an important consideration. However, it's not weird, nor is it really your concern. No doubt the event organizer has an injury waiver signed by the parent of each child, before they can participate. They should also be including a clause about photos being taken at the event and made publicly accessible (published, as in posted on the Internet where anyone can view them). This is getting to be a standard clause in the waiver forms at all the events I work with. If not, I certainly would encourage the organizer to include it! It covers them, more than me. No, I don't use passwords on event galleries, anymore than someone would need "a password" to walk up and sit down on the bleachers to watch the event.
Regarding image theft... Just don't put larger than thumbnails online, then there's really not much for people to rip off!
If the organizer has a web page, get them to post a link to your photo galleries on it. This is critical to help drive traffic and sales. Again, allow them to use some of your photos, such as on their web page.
We also sometimes offer onsite printing (for those impulse buyers in the heat of the moment!). This usually doubles sales for most events. People forget to go to your online galleries later, lose your biz card, etc. If you rely only on online sales, I think you leave about half the money on the table uncollected.
However, there's a cost to offering onsite printing, at larger events. First, you need someone to handle the sales and printing for you, because you'll be busy shooting. At a minimum you need computer equipment and a printer, some chairs, a table or two, and perhaps a popup tent. You'll need to print out thumbnail catalogs on the spot for people to look through, or provide a second computer monitor (or several) for them to review your images. A dye sub printer is fastest, but ones that can handle 8x10 aren't cheap. We make do with inkjet, and charge a small premium even though online images have had more editing and tweaking done. We only offer 4x6, 5x7 and 8x10 glossy prints onsite.
You have to weigh the fact that you might double your sales, against the cost of setting up to print onsite.
Later, when editing, do printout thumbnail catalogs of the images, organized exactly the same way your images are online. Take these with you to subsequent events. People love to look through them and often place orders.
I'm looking into an onsite "virtual kiosk", which is more of a self-service set up. It will involve a computer server and several satellites with monitors where people can view thumbnails of the day's shoot (added throughout the day, still working on the workflow for this, though). They can then place an order themselves right on the spot, which is fulfilled later through Printroom. Initially this would probably be in conjunction with onsite printing, but eventually perhaps it could replace it entirely. Of course, there's some cost involved in this, so it's not something anyone should jump into right away!
You probably won't get rich, but it can be a lot of fun and can generate some revenues to buy a new lens or something neat like that. Oh, and someone mentioned being disappointed in sales... well, frankly I think a lot of people are feeling the pinch of gasoline and milk costs, and just being cautious right now. So, sales have been soft the past 6 months or so, but this will vary from one place to the next.
Finally, if you find established event photographers working in you area, it might be a good idea to work with one and learn the business as a second shooter, before jumping in with both feet and possibly going over your head in the proverbial deep end.
It sounds like you have an potentially untapped market, so after you check around for any direct competition before investing too much effort or money, I say go for it!