I sowed the seeds 11 days ago. As soon as they germinated, I placed them by a SW-facing window, where they receive direct sunlight all day. I'm no expert, but they appear to be healthy. I just can't tell if the stems should be thicker at this point. The tallest plant is 2 1/4 in. tall.
Leggy just means there's a lot of stem in the internodes (and between the soil and the cotyledons, too). Internodes are the parts of the stem between the parts where the leaves are growing. They do look somewhat leggy, but that doesn't mean they're unhealthy. It could mean they don't have enough light, but it sounds like they have plenty (they might need more than you realize, though). So, it probably just means they have a good supply of phosphorus and/or maybe warm temperatures. I wouldn't worry about it, though. When you transplant, just bury the stem a little deeper than you would for a less leggy plant.