I started the sunflower seeds in a seed starter kit, they came up within 3 days and then I put the little plants on bigger pots. They are growing by leaps and bounds but not straight up! What did I do wrong? The plants now are about 12" but they are fallen over and up. Please help!!

Did you just repot them? If you did, then they are probably going through the shock of being repotted, and it will take some time for them to get over that.

What kind of sunflowers are they?

Sunflowers will do best if they are outside in the ground and getting lots of warm sunshine.

Where are you located?

If you are unable to put them into the ground, then putting them into a very sunny window might help. But, depending on the kind of sunflowers you have, you may need to keep repotting them as they continue to grow and they aren't going to like the continued shock of being repotted.

Thanks for the prompt response. They have always been outside as I am in Miami, Florida and the weather is warm.

I found the following information on the site link Growing Sunflowers - The Sunflower Stop that you also might find to be helpful to you.

Soil Considerations

Sunflower plants are like any other plant. The better the soil the more heartier and robust the plant. Our experience shows that sunflowers like a soil that drains well and contains a lot of mulch. About two weeks before planting I mix a bit of steer manure into the soil where I am going to plant.
Sunflowers do well in many different soil conditions, so I would not get too hung up on your soil conditions. If you have plants that are doing well now in an area where you want to plant your sunflowers, then your sunflowers will do just as well.

Sun and Water

The operative word here is sun. Like its name the sunflower needs plenty of direct sun; a minimum of 6 hours a day to grow healthy plants. If you plant sunflowers out of direct sun light they will stretch for the sun. They will become so spindly stretching for the sun eventually they will fall to the ground. We recommend full sun for the better part of the day to grow strong healthy sunflowers.

Stake them... even in the pot just get a small stick, dowel etc... and tie them lightly to the stick... this will help them grow upright... sorry clough if I am repeating any of your info.

The plants are outside although in shade in my patio. I think it is too late now to stake them. They will probably break when I do. I will try again with new seeds. When do you recommend to stake them? I did put some in the ground in the sun among other plants and they are also laying on the ground. I thought perhaps their roots are too week. The plants are now about 12" and growing in waves. Thanks to all that have responded to my question. Sounds like I will have to start over again.

They should still be bendable at this point... I would still give it a try. If I started over, I would start with a bigger pot than the little starter one's and when they about 4 inches I would just take a piece of old towel or other cotton material.cut into strips.. something that will not cut into the tiny plant and stake them to a skewer, dowel or stick that way they can grow upward... then transplant them... even then you will probably need to stake them for a while... I like to use paper milk boxes, styrofoam cups something that I can easily tear so that I can leave the dirt intact... now if you leave them in the pots for a while and it forms a root ball you will need to break it apart so that it will take growth to the new soil. But you will be able to visually tell that as soon as you release them from the container.