They look healthy. It's not unusual for seedlings to temporarily stop growing for a while a few weeks after germination. I might speculate it's because they've used the food storage in the seed and need to start producing their own food by photosynthesis before they can grow some more. Or maybe they're focusing on root growth for a while. Whatever the reason, as long as they're as green and healthy looking as they are now I wouldn't be worried about them.
Edited to add that you also transplanted the first one and that too may cause it to take a break while it recovers depending how much, if any, root damage ocurred in the process.
