If your baby is born in the late summer or early fall, there’s a good chance there isn’t going to be much of anything about her first Halloween that’s going to spook her. Not because she is stone-cold hard to scare, but because until your baby is somewhere between 7 and 9 months old, she may get startled, but her understanding of the world hasn't developed to the point of real fear.
Before she starts to develop fear, your baby can still feel unhappy, and probably has no problems telling you all about that unhappiness, even though she is still a little short of having the words for it. Somewhere in the 7 to 9 months range, though, a few things start to change for your baby. She doesn’t start to feel fear all at once, and while everyone develops different fears as they get older, during young childhood there are fears that tend to come with different developmental stages.
A baby's first fear is generally a fear or anxiety of strangers, which develops around 6 or 7 months old as she develops the understanding of the differences between her parents and everybody else. The combination of stranger anxiety and object permanence can lead to separation anxiety, and can make leaving your baby with a caregiver, or even just socializing with people who are familiar to her but aren’t her immediate family, more difficult.
Luckily, this phase does pass, though it can be as short as a few months, or can last up until your baby is approaching her second birthday. The best way to handle it is to reassure your baby that while you may leave her, you’ll be coming back. You can do this both by talking to her from the other room as you leave her in a different part of the house, and by telling her where you’re going and when you’ll be back when leaving her for longer periods of time, and then following through on that promise. The best way to handle her stranger anxiety is to let her get to know herself the people who make her nervous slowly, quietly, and preferably from the safety of your arms. You can explain to friends or relatives who your baby never had a problem with before that it’s nothing personal, and that she will probably readjust to them quickly, especially if they don’t force it.
Another way to help your baby feel at ease in social situations is just by being comfortable yourself. Babies pick up on many fears from their caregivers, and facial expressions are one of the biggest giveaways you have. your baby has been able to mirror faces back at you since shortly after birth, and since that time, this mirroring has developed into social referencing, which means your baby looking to her parents or primary caregiver for cues about how to react to a situation. This means that if you’re nervous walking into a party, your baby will probably be nervous, too, and will have a harder time opening up to the new people she meets.
Because of this kind of unconscious communication, very young children are in a perfect position to inherit their parents’ fears. This isn’t always bad, since fear can be an important tool to keep your baby safe from dangerous situations, but it can backfire if she starts picking up on any less rational fears you might have.
When babies first learn to crawl, they can crawl themselves into some dangerous situations, like almost off of changing tables, beds, or any unattended stairs, because they haven’t yet developed a fear of heights. Babies develop depth perception sometime around 3 or 4 months old, but don’t develop the fear of what that depth and height could do until they start crawling, scooting, or otherwise moving themselves around. When babies are carried, they don’t tend to pay much attention to what’s going on in their peripheral vision, so it isn’t until they start moving on their own that they start to register the way the world around them seems to be moving ‘backwards’ as they move forward, which seems to trigger their first fear of falling.
your baby’s fears aren’t themselves developmental processes, but they are triggered by them. The more your baby understands about the world, the better she will understand its dangers, so her growing fears are signs of her involvement and interest in the world around her.