While having the accounts at the same place as you do is nice, it's not that bad if they're at different places since you can set up electronic transfers and do everything on the web these days.
My stuff is at Vanguard but when I opened Roths for my kids Vanguard wasn't very supportive of small account balances. Because of that, and because there was a local office that we could physically go to if the kids had questions and to drop off the initial checks, they ended up with accounts at Schwab.
I thought that the lower cost at Vanguard would result in them moving from Schwab to Vanguard at some point. However, the investments my kids have at Schwab are already very low cost and it is dropping over time, so that's not a real concern any more.
On the bank account side, you can either go with an online bank that does offer better interest rates, or a local bank where the kids can get the experience of dealing with tellers and branch managers in person - which, although it may be going away, I still think is a good experience to have. My kids currently all bank locally. Oddly, they have accounts at three different banks. Again, with electronic transfers and Paypal and such, it is pretty easy to manage.