Welcome to Websleuths, rekabal! Good to have you here
I think someone could just not get routine medical care, and if the baby got very sick, take him to an emergency room, where the focus would be on the baby's immediate medical crisis. Lack of medical records could be passed off and distracted from. "Oh we just rushed here and we just moved into town - I didn't even bring my purse with me! I think I may have lost his medical and shot records in the move! Is he okay, doctor? What's wrong with him?". A particularly manipulative person might even be able to convince a doctor to bring the baby's shots up to date.
At some point though, I would think lack of regular medical care and shots etc would be bound to start causing health problems that a doctor or nurse would start questioning. But then, whoever had Gabe could just move out of town.
ITA. That's why I suggested that one of the people who has Gabe might be a Dr. or know someone who is a Dr. that would keep things quiet and still administer medical care to Gabriel. I'd like to add to that now and say that it could even just be someone who has medical background and/or access to supplies like immunizations, prescription notepads, etc.
In a worse scenario, these people did not want Gabriel to love as their own, but are using him for nefarious purposes, in which case, they would not care a lick about his medical care.
I'm very concerned about Gabriel's situation. My son had to see his Dr. every 2 months until he was 9 months old, and now he doesn't have to go again until his 1st birthday. At 8 or 9 months, they typically receive the last of their immunizations until they are 12 months. At 12 months, they receive more immunizations including their MMR.
Since Gabriel went missing before 8 months, I'd wager a guess that he is overdue for some of these immunizations already.
The immunizations don't concern me as much as the thought that his progress is not being followed by a Dr. The first year is SO important on many levels. Dr's chart the child's growth patterns based on their own curve and also what would be normal for a child their age. They watch to make sure they are growing in length, weight, and head size properly. If the baby is not following his/her curve properly, it can be an indicator of different problems that should be looked into. They also keep an eye on nutrition and things like if they have good fat layering, if they are on par with their milestones, etc.
Gabriel went missing at a time when many babies start having seperation anxiety, are learning object permanence (meaning they know a person or object still exists even though they can't see it), and tend to become clingy to one or both parents. I'm concerned about how this has effected him mentally and emotionally.
BTW, Welcome to WS Rekabal!!! Glad to have you join us.