I needed a slider like this for the sim kids so here it is for anyone who'd like to have it as well.
In the image you can see the kid on the left without this slider affecting at all, and on the
right the slider is on the maximum limit. So you can change the chin to neck line between that range.

This slider is familiar if you know Heiret's chin to neck line slider - apparently it isn't working for children, so
I made this slider so you can make that little change of shaping the chin to neck line for kids too.


NOTE:

*The neck looks a bit odd with a little bump, because I can't move the vertices on that area or the head and body will not be aligned.

*This affects only CHILD (CU) so no toddlers or others. When the sim grows up this slider does not affect anymore, but then you can move on to use Heiret's chin to neck line. You can get heiret's slider here if you do not have it and are interested: http://blog.naver.com/ginami97/107402943

Location:
You can find this slider in CAS panel of head and ears, in chin settings.



Install instruction:
Just put this slider into My documents/Electronic art/The sims 3/mods/packages folder,
If you do not like the slider, just remove it and that's all.

Additional Credits:
Lapiz Laluli for the hair, WM for the skin and CmarNYC for morph maker, and all the other sims' tool creators.