No. Gabriel is two years old, not 3-4 MONTHS old. This is the only family he's known. He loves them and they love him and want to adopt him. Can you imagine what it's going to do to him psychologically to be ripped away from them?
Grandma in Mexico has known about Gabriel since his birth. Why didn't she petition to take him then?
The article says that she didn't know until a year ago that the baby existed. At that time she might have thought that this was the best temporary solution until the child's mother rehabilitated herself and took back the child, but now she finds that the foster parents plan to adopt and keep the child.
It takes a special person to be a foster parent. You have to remember ALWAYS that you are only the temporary caregiver for the child and that you can and will be expected to hand the child over to his blood family at any time. It is your job to facilate that hand over and make it easier for the child, not block it out of selfish reasons.
It will be initially hard for the child if they don't prepare him by reinforcing the idea that they are not abandoning him, but sending him to his own grandma that loves him as much as they do. They need to get across in their actions and words that his grandmother loves him as much as they do and that she is not a person that is ripping him away from the only people that love him. The grandmother seems to be thinking of the best interest of the child because she doesn't wish to cut the foster's parents totally out of the child's life.