Have you checked out www.twowheelingtots.com yet? That site is amazing when it comes to details and comparisons, and does a good job of characterizing what bikes are good for what kind of riders and gives height and inseam recommendations that I have found spot-on. Quality kids’ bikes have come a long, long way. Interestingly, with a few notable exceptions like Norco and Raleigh, by and large bike shop kids’ bikes aren’t usually the best choices – companies that build bikes for kids and only for kids have been really really thoughtful in their designs.
Most 7-year-olds are going to be on a 20 inch (wheel size) bike unless they are particularly tall and can handle a 24 inch.
Most of the online-only companies have a test ride period where bikes can be returned, but every bike I have bought on the advice of TWT has been a winner. We have (had) a 14in Islabike, a 16in Priority Start, a 20in Guardian, and a 24in Raleigh Cadent in the stable so I feel like we’ve really had a pretty broad representative sample. They aren’t cheap, but they hold their value well – we’ve been able to sell the ones we’re done with for almost as much as we bought them for to fund the next step up.
Just to warn you, kids’ bikes are in short supply right now. Pandemic problems!