I took my son's 6 Volt Paw Patrol Fire Truck Ride On Toy by Kid Trax and upgraded it to have two 24 Volt motors. Below are the parts and tools that I used.
Tools:
Flathead Screwdriver
Soldering Iron and solder
17 mm socket with wrench
Wire strippers
Electrical tape
Parts:
Drill battery adapter for Kobalt 24V batteries: https://www.amazon.com/dp/B0D4H5RR6N?ref=ppx_yo2ov_dt_b_fed_asin_title
12 gauge speaker wire: https://www.amazon.com/dp/B0CXJLNCGP?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1
24 Volt motors with wheel hub: https://www.amazon.com/dp/B0DH1FGXCL?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1