Chimporazo and Peter;
I have to differ with you on this. 
First off, if children ONLY speaks spanish, then it means that they either are younger than 5/6, OR have just recently got here. 
Now, assuming that the parents are illegals, it would require that the child less than 5/6 has NOT assimilated in any form into our nation. 
Likewise, if the older child was brought here and has not learned to speak english, then they also have not assimilated and are still tied to the parents nations. 
IOW, in those cases, I do not believe that it is right to allow them to stay. 
The reason is that it will NOT hurt the child(ren) to go back since they have not assimilated. 
OTOH, if a child has attended school for say 3-5 years, they are assimilated and will see themselves as being Americans. Then it is not fair to them to send back unless they are total losers.