The Datura? I pot em up when they have 2 sets of true leaves. I went to 3 or 4 " pots and at about a foot tall move to larger pots - 5 or 6". From my experience, I have found that Datura do not seem to want or need the very larger plants that Brugs need.
The Datura can grow very quickly. The 3 types I have grown went from seed to bloom in about 5 - 6 months.
Do you know which of the Datura have germinated?
The Datura are very fertile and will make a lot of seeds. My experience has been close to every single flower makes seeds.