[A_mothers_love]

It must be difficult for you to be parenting and then to have to make this type of decision. My heart goes out to you. As hard as it may sound tell your children the truth, If you feel that you daughter will feel guilty this is my suggestion;
Tell your oldest daughter that you gave your child up for adoption because you needed to concentrate on them, that though your baby is important to you, you know that he/she will be well cared for and your main concern at this time was to see to the daily needs of your other children, I dont believe saying that you couldnt afford to keep your baby would go over well for a young adult (teen) your other children, tell them in age appropriate words the same thing, that even though you love your new baby you have a responsibility to see that your other children do not suffer.
Dont use financial reasons until they understand finances.
Hugs
Melissa