Willeke, Your seedlings are looking tremendous. Have they ever grown. When time to put outside and in their own little pots, they will put on even more.
Sometimes as seedlings they may look tall, but many reach a point and will start to fatten up in girth. Usually it is when they have 6 true leaves and terminal growth point looks like it is shooting to the sky. These are the ones that will become leggy.
So wonderful. Looks nice outside there for you. Hope your summer starts early for you.
Rick