new motor can't hurt! I bought a used power wheel and new motors helped that out but it was several years old. I'd try adding a second battery first personally.

I don't have any experience with Kid Trax but if they are anything like power wheels then the stock battery takes up extra space. I bought a 12v battery off of amazon with a new wiring harness and it has more MAH (longer run time) and takes up the same space as the stock battery.

Amazon has a replacement 12v battery with harness for 80 bucks, or you could get just the harness for $15 and a 12v better for $22 instead. I have only used the "expert power" brand and it has been working fine for me. best of luck and let us know how it goes!

harness

https://www.amazon.com/Battery-Connector-Harness-Replacement-Parts/dp/B07F9Q345N/ref=sr_1_14?crid=15JVXXJPEYNPG&keywords=kid+trax+12v+battery&qid=1578341186&sprefix=kid+trax+%2Caps%2C182&sr=8-14

battery

https://www.amazon.com/ExpertPower-EXP1270-Rechargeable-Lead-Battery/dp/B003S1RQ2S/ref=sr_1_4?crid=22FI8JFEI3GHP&keywords=12v+7ah+battery&qid=1578341327&sprefix=12v+7ah%2Caps%2C174&sr=8-4