Good morning.

I have recently started growing some bonsai trees, and I have some Black pine seeds that have started growing. But the seedlings seem to be collapsing under the weight of the head.

am I supposed to put a stick or something in to support the seedling as it grows.

Thanks
Dan

Hello and welcome.
a picture would help but an educated guess tells me that it is probably inside and because of a lack of light became to leggy and weak ( correct me if i'm wrong). Without any doubt it will die inside ( if it is inside)
But as i said, a picture and a bit more info about your care would help. Btw, you are not growing a bonsai tree but a normal tree which can be turned into a bonsai in time ( about 20 years) and a lot of ( sometimes difficult) techniques executed on specific times during the year, depending on the tree itself...