In Campaign Manager 360, after setting up your coffee store chain client with separate child advertisers, the next step to prepare their account is to develop a campaign for their new latte product.

• Upload the specific creatives for the latte product into their account.
• Choose the desired ad sizes for the latte product-related creatives.
• Develop a campaign for their new latte product.
• Select optimal placements for their latte product launch.

The correct answer is: Develop a campaign for their new latte product.

Explanation: After establishing child advertisers for a coffee store chain in Campaign Manager 360, the next step is to prepare the account for active advertising. Child advertisers segment the account, but a campaign is needed for specific promotions. Thus, developing a campaign for their new latte product is the logical next step. This campaign will organize placements, ads, and creatives, allowing for focused tracking and optimization. By creating a campaign, the account manager moves beyond organizational setup to actual campaign execution, ensuring the new latte product receives targeted promotion within CM360.