I got Brothers SE 400 and struggling to learn for embroidery. I read lot of them online.  I am new to this forum and would like to ask you all about better stabilizers for children's t-shirts. I heard about light, medium and heavy weight. Are they awesome to use? Please let me know. 

Ballpoint needle is overwhelming for knit fabrics and always use an iron-on stabilizer for knits. Two layers might be necessary if the design is dense.

Not really, ballpoint needle also cannot perform the task very well. Last night, I tried it but I got hole in the t-shirt. 

 You can search some of the lesson appropriate for embroidery designs. Here is one of the and i hope it helps you

 

http://www.emblibrary.com/EL/elprojects/Projects.aspx?cs_productid=pr1334&cs_catalog=elprojects

For t-shirt and onesies, I personally recommend medium weight cut away. That should be even or uneven. This helps (threads) to provide excellent registration. For receiving enhanced output, you should stitch t-shirt etc. to the stabilizer before design stitching. I would say, better, try out test stitching on a t-shirt before starting actual one. 

You can go http://www.designsbysick.com/backings.php for finding appropriate design. I love them very much. It has very high-quality stitching capacity. You should have sprayed to attach fabric rather using stabilizer that does not iron very well.