Humans go through a lot of development in the early years of life, but it may surprise you just how weird some of those changes are. Did you know, for example, that you actually lose about half of your brain neurons in utero through a process called apoptosis? And that's even before you're born! Scientists think that apoptosis is important because it helps your brain make the right neuronal connections. As a child, you have a lot more neuronal connections than you actually don't need, which means that unless you are actively fine-tuning those synaptic connections, apoptosis will make many neurons die-off naturally. Ultimately this process is critical during childhood because it makes way for new, more important, synapses.
Another surprise development that might be news to you is the ability to shiver. You don't actually come out with the ability to shiver because it isn't until the age of around 3 months that you have developed the muscle tissue to do so. In order to keep warm, young babies have a special kind of fat called brown fat, that has more blood vessels and and mitochondria, which they burn when they get cold. This process is called nonshivering thermogenesis!
And just to keep you on your toes, did you know that your larynx actually drops from your head down into your throat? Your larynx helps you breathe without inhaling your food by closing the epiglottis so that food can reach your stomach. It's also important that the larynx is in its permanent anatomical location in your throat because it helps you articulate many different sounds which are necessary for language!