Hello.
It is common for DC motors like these to briefly draw spikes of current up to their stall current when driven at 100% duty cycle from rest. If you are switching between full-speed in one direction to full-speed in the other direction, you could see spikes upwards of twice the stall current. These spikes are very brief, but if you are concerned about them or they are causing problems, you might try implementing some acceleration ramping.
By the way, it sounds like you might be planning on using two voltage regulators with their outputs paralleled; please note that we do not recommend paralleling regulators like that. You can find more details about that in this forum thread. but it is typically better to use a single step-down regulator that can handle the current draw of your application.
Brandon