"Children develop separation anxiety. They have a bond with their primary caregiver, parent, or babysitter, with whom they are familiar and feel safe with," Dr. Alison Mitzner, a pediatrician, tells Romper. "When their caregiver is gone they become upset and are then comforted once they return." Mitzner says older babies and toddlers in the second year often cry and get "clingy" when their parents or caregivers leave the room or the home.

The child may not want to be with others at all and may cry when another person tries to hold them. This is all very normal and, as suggested on WebMD, parents or caregivers should never sneak out of a room or leave when their baby is hungry or tired. The best thing you can do is remind them you'll be back and not make a big emotional show out of it.

"When a mother leaves a baby, even for a short time, the baby's limbic system or the part of the brain that responds to stress is alerted," Erica Komisar, psychoanalyst and author, tells Romper. "The hypothalmic-pituitary-adrenal (HPA) axis responds to the stressful event by sending cortisol or stress hormones to the baby's body so the baby is now in a defensive or hyper vigilant state."

The good news, as Komisar explains, is that if the baby is left alone for a short time they'll be able to handle it just fine and recover.

If you leave the room, your baby or toddler will think you've left for good. As heartbreaking as that is to think about, Mitzner says it's just that they don't understand yet that you'll come back. She explains:

There is something called object permanence and they haven’t developed yet. Object permanence is the understanding that objects still exist even if they cannot be seen. Babies don’t understand that something exists even when it leaves the room or moves away. If they can’t see it, they think it is gone.

Your baby might even cry if you walk into a nearby room, because they don't realize what's happening. Rest assured, it's completely normal. You might not be able to teach your baby to be more independent (they're just not developed that way yet), but you can start to practice incremental times of absence and see how it goes.

"Nighttime security is the most important time for a mother to reassure her baby of her presence since it is at night that a baby is most frightened of separation," Komisar says. "Sleep training, if imposed too early, can effect a baby's emotional security."

She says the first six months of a baby's life needs to be filled with moments where a parent or caregiver is reassuring them whenever they cry. As the child becomes more emotionally secure then "a gentle sleep education can be implemented," Komisar says.

"The amygdala, a small almond shaped part of the limbic system, when first confronted with stress can enlarge," Komisar explains. "But if exposed to prolong stress can in theory shrink impacting the baby's ability to regulate his emotions."

There is plenty of debate and different schools of thought on whether or not a baby should even get to the point of crying in the first place. And if they do end up crying, there's the question of how long you should let it go on for. Probably one of the most compelling arguments surrounding this debate is that distress for too long in babies can actually kill brain synapses, or brain networks, which are growing at a fast rate, according to an article in Psychology Today. Basically if you have a chronically distressed baby who doesn't develop emotional stability, you're raising a disagreeable adult who can't handle their emotions properly (or so the explanation goes).

So the key is figuring out how to reduce the amount of time your baby is distressed. Part of that is determining how long your child can handle being away from you, but the other piece is identifying caregivers they feel comfortable with in your absence or when you have to leave them for more than a couple of minutes at a time. No one can take your place, but they can create a safe, happy environment until your baby is in your arms again.