Taxable investment account questions -?

So I would like to put my and my kids savings into investment accounts. I am planning to keep most of the money in vanguard index funds but I want the flexibility to be able to buy some specific stocks and possibly bonds. I was going to open a vanguard account and a online brokerage account with scott trade. Do I need to do this (open multiple accounts), or can I buy vanguard funds from the scott trade? What's the advantage of dealing direct with vanguard? I know about the minimum 3k to open one. Thanks -