Please find rules for claiming a dependent in IRS publication 501 page 12 - http://www.irs.gov/pub/irs-pdf/p501.pdf
I put extract here for your convenience
So if the child is not related to you - the child is not your qualified child, but may be your qualified relative if the child is not a qualified child for anybody else and lived with you whole year.
In this case - you might be eligible to claim the child as a dependent.
Let me know if you need any help.
Seems as the child did not live with the mother at least 6 months and is not her qualified child for tax purposes.
If the child is placed with you by an authorized placement agency or by judgment, decree, or other order of any court of competent jurisdiction - the child is your qualified child and may be claimed as such.
If the child is not placed with you by an authorized placement agency - the child may be only your qualified relative - but has to live with your whole 2009 year - if the child lived with you less then the whole year - the unrelated child may not be your qualified relative.
To claim the child in this situation - you need to obtain an authorized placement, or decree, or other order of any court of competent jurisdiction.
If you qualify - you may claim a dependent filing tax return online - it doesn't matter if your dependent is a qualified child or a qualified relative to be able to file online.
You do not need to provide any documentation to the IRS - unless the IRS asks to proof qualifications for claiming a dependent.
All supporting documents you need to keep with a copy of your tax return - and should be able to provide to the IRS if requested - but do not send with your tax return.
The IRS doesn't use the term "qualifying dependent"
You are claiming a DEPENDENT.
To be your dependent - the person must be either your qualifying child or a qualifying relative.
Please see definition for each above.
Claiming dependents with complex names is a headache.
Generally it should much whatever the IRS has in their system. In most situations it is the same which is listed on the social security card.
I would enter the full name and submit.
If for whatever reason that will be rejected - try to resubmit using the first part only.
Than what we usually do with complex names.
Sorry - there is no simple solution.