A rectangular 9v "transistor radio" battery is entirely unsuitable for powering motors. Not only would it run down in no time and be expensive for the amount of energy provided, it has such a high internal impedance that the voltage would sag beyond the point of effectiveness when connected to the low impedance load of a motor. For the motors you have, you will instead need at minimum a pack made of a number of quality AA cells.
A lossy bipolar driver like the L293D or L298 is also an absolutely terrible choice for a low voltage project like this, though unfortunately historically popular and still showing up undeserved in "motor shields" to this day, so you can't really be blamed for trying to use it. Consider looking at an FET driver like the TB6612FNG. If you do stick with the L293D in the short term, you'll probably need one or two extra AA's in your battery pack just to accommodate its losses.
But before you change anything, see how your motors perform if directly wired to a 4 cell AA battery pack. If they have a bit more power than you desire, a good low loss FET driver capable of handling their current, and PWM speed control, will let you tame things down and operate as desired.
If the motors don't exceed your power needs when directly connected to the battery, things will only get worse with the driver. In that case you need to add another cell or two to the battery, get cells with lower impedance, or consider a different motor choice.
I built a tracked RC toy for my nephew a year ago using motors visually similar to yours driven by a TB6612FNG. It performs quite nicely on 4 new alkaline AA's though it's a bit slow with the lower voltage of NiMH - if I did it over, I'd probably design for 5 NiMH cells. However as the same plastic gearbox is offered with a range of different windings on the motor installed, your specific experience may vary a little. The lowest voltage motors offered in those gearboxes would probably benefit from more current than a TB6612FNG can continuously provide.