Do we need to worry about capital gains if we did not receive a 1099-B for our account with Vanguard?

You only receive a 1099-B when you sell the stock and realize the gain or if you had taxable dividends that would be reported on a 1099-DIV.

If you had taxable dividends, or Capital Gains Distributions (CGD) , in a mutual fund, it  will be reported on a 1099-DIV, not a 1099-B.  Dividends are in boxes 1a & 1b and CGD in box 2a.

It does need to be reported.  TurboTax will pick it up from the 1099-DIV and enter both in the right places. CGD and "qualified" dividends are both taxed at long term capital gains tax rates.

You can download your tax forms from the Vanguard website.  Just login to your Vanguard account.