Obviously, yes. What makes you think that someone will invest a lot of time, effort and resources on the developing of a design/item and that anyone will be able to just jump on the money wagon and make a profit out of it? Rule of thumb: popular items are always ip protected.

You may wish to learn about USPTO. It is a government website. You can search trademarks to your hearts content.

Your question seems odd. You should be sourcing your product from an authorized distributor. You should also have approval to sell them on Amazon.

If you purchased the items from a retail store, you will fail when Amazon requests you to provide invoices.

You will need a Letter of Authorization from the Brand Owner. You will also need to have other government certificates related to all toys offered for sale in the US. You will also need a manufacturer’s invoice. You will also need laboratory tests that show it’s safe for kids.

More to consider other than just the popularity.