Try leaving them to grow on a bit larger instead of moving, to get some decent roots on them first

Thank you for that I will give it a go.

As suggested, try leaving them a little longer before potting on. Use 9cm pots and plant them deep but only handle by the leaves and not the stems. Somtimes you can get a packet of seeds which are of poor quality so perhaps if this continues you could email the seed merchant and ask for a replacement.

Bad seeds wouldn't sprout at all. Are the seedlings getting plenty of light? Stretched out, light starved seedlings will have a tough time adapting to separation and repotting.

Thank you for that Tugrethil, I thought that they were gettin to much direct sunlight so I put up a net defuser up where they were in the greenhouse but they the still keeled over. I will try again next year but with a differant compost and leave them in longer. What do you mean Stretched out?

Seedlings without enough light look like a bowl of spaghetti, with 2-6 inches of stem from the ground level to the seed leaves. Ideal is less than an inch. I would plant the seeds where they can get at least a half day of direct sun from before they sprout.

Thank you for that Tugbrethil I will try that next time I sow some seeds.