Chemical reactions and catalysts. A chemical reaction involves a chemical change, which happens when two or more particles (which can be molecules, atoms or ions) interact. For example, when iron and oxygen react, they change to a new substance, iron oxide (rust).
It's important for parents to start weaning babies from bottles around the end of the first year and start getting them comfortable drinking from cups. The longer parents wait to start the transition, the more attached kids become to their bottles and the more difficult it can be to break the bottle habit.
When to wean is a personal decision. A mom might be influenced by a return to work, her health or the baby's, or simply a feeling that the time is right. Weaning a baby is a gradual process that calls for patience and understanding from both you and your child.