Your growth is a little slow, biggest newbie mistake is over watering it seriously stunts growth, especially when they are little like that and are in a critical period of development. I lost about 2 weeks worth of growth with mine in the beginning, it sucks. Don't be afraid to leave them alone and let that soil get DRY as all hell. Even if you have 6 inches deep of dirt and the top 3 inches are dry, there's still enough moisture down there to keep the plant from dying. The best advice I got was to check by weight: whenever you water, lift and feel how heavy the pot is. When its gotten significantly lighter, about 50% or so then water it again. With those little cups you are using (the biodegradable ones are what it looks like) you probably could water something that small once a day, or every 36 hours.
But yeah, for some reason your plant isn't producing the sugars that it needs to start exploding. That means that you probably have a problem with air or light, who knows. Some details would really help. In hydro growth can be stunted by pH being off, BC the plant can't uptake its nutrients and produce its food. That problem is a lot more rare in soil so I doubt that's what's going on.
BTW, just stick a toothpick Diagonal down in the dirt at the base of the stem to prop the plant up. But you really wanna get some fans blowing on those plants BC the movement that it gives them tears their little plant tissues and makes them stronger, sturdier, and able to hold more weight, which winds up equaling more bud
Good look bro just keep on growing. Study up and keep tweaking your setup, you'll get it dialed in and you'll absolutely love it when you do. If it was Those plants would be at least 6-8 inches already, and if you started from clones they would be ready to go into flower