Baby shampoo is a gentle hair treatment for infants and toddlers that is used to bathe the child. It's designed to reduce tears while cleaning, prevent skin irritation, moisturize hair & scalp, nourish & cleanse the hair. Some formulas may be tear-free but this does not mean they are less effective or suitably milder, it just means that the product is less likely to cause stinging or burning of the eyes if it were to come into contact with them.
The baby shampoo contains mild cleansing agents, some form of fragrance (essential oils), thickening agents, and preservatives amongst other things. The main ingredients that are responsible for the cleaning action of baby shampoo are sodium lauryl sulfate or similar agents. They produce a lot of bubbles and give your children's hair a good thorough wash. Some baby shampoos may contain oatmeal or other ingredients such as aloe vera, chamomile extract, and vitamin E which would help with dry skin and dandruff. Always check the label before purchasing a shampoo to make sure you're aware of exactly what it contains.
Baby shampoo is generally designed and manufactured for the specific requirements of infants and toddlers. It has a milder formula than adult shampoo as it contains many other chemicals that cause skin irritation. These other chemicals are used to make adults' hair shiny or moisturized but can be extremely harmful if they come into contact with your child's eyes, mouth, or open sores such as nappy rash.
For these reasons, it's preferable to use baby shampoo instead of whatever you happen to be using at the moment. Never use adults' shampoos on your child as they can cause skin irritation and may not be suitable for infants and toddlers to swallow (this is especially important if you're bathing your child in a bathtub).