Stems are bending/snappig

Hi this is my 1st time and I've got a few 4-7 days old put they seem to be bending/snapping over by themselfs over night i had 4 any help!!!??? they are outside in a greenhouse and just changed to a bigger plant pot and some quality soil. Any help will be very much appreciated

Sounds like they need more light.

Edit: Be sure to wash your hands well before dealing with seedlings.

I've had similar with seedlings.

Firstly, am I reading you right that your seedlings are 4-7 days old and you have just transplanted them?

That may be your first causal factor. The seedlings needs to be a little stronger, from being older, before you can risk transplanting them. (if I'm reading you wrong then ignore this)

Regardless of the cause, it needs sorting. What I do is to get a drinking straw, cut one end into a point (this will be dug into the soil). Cut the straw open, maybe even cut out a narrow slit, and then position it around the bent seedling, digging the pointed end into the soil gently and as far as it will go. The straw needs to be about 2/3rd's as tall as the seedling. It will be supported and rest on the straw.

This may not be relevant advice, pictures would really help.