Bid has two main meanings that kids often encounter:

1. To offer to pay a certain amount of money for something, especially at an auction. At an auction, people bid on items they want to buy, each person offering more money than the last until someone wins with the highest bid. You might see this at a charity auction where parents bid on gift baskets, or in online auctions where collectors bid on rare baseball cards. The person who makes a bid is called a bidder, and the amount they offer is their bid. If you bid $50 for something and someone else bids $60, they've outbid you.
2. To make an attempt or effort to achieve something. A team might make a bid for the championship, meaning they're trying hard to win it. A politician makes a bid for office when running in an election. When your older sister makes a bid for more independence by asking to walk to school alone, she's attempting to gain something she wants. This kind of bid is about striving and competing, similar to an auction where you compete with others.