Welcome to QuickBooks Community, Ashleynd. I'll share some steps to ensure you're able to set up the petty cash account with a starting balance. I suggest going to the Chart of Accounts page. From there, you'll have the option to create a new account which will be named Petty Cash by clicking the New button.

Here's how:

1. Go to the Gear icon ⚙ and select Chart of Accounts.
2. Click the New button.
3. From the Account Type drop-down, choose Bank.
4. In the Detail Type drop-down arrow, choose Cash on hand.
5. Enter Petty Cash for the account name.
6. The opening balance will be created when you move money from the checking account by writing a check or transferring funds. If you already have money to use for petty cash, enter the amount in the Balance field and choose the as of date.
7. Fill in the other necessary field.
8. Hit Save and Close.

For additional information, you can refer to this article: Set up and use petty cash. This also provides details on how to manage petty cash in QuickBooks Online.

I'm adding this article to further guide you in effectively managing your business using QBO: Help guide for QuickBooks Online. It contains topics about advanced accounting, banking, and payments to name a few.

Let me know if there's anything else you need help with. Know that I'm always here to help you anytime. Take care and keep safe!