My children asked me to buy a car for them to drive. Then I decided to make one myself sothat children will also learn during the process. Looked a few designs on internet and drafted my design as a simple one.

Bought a square pipe(hollow) of approx 20 feet to cut it and make frame of the car.

I bought 4 exide batteries of 12V-42 Amps each.

Supplies

Square pipe 20 feet
Electric motor with controller 1200 W (used in E rickshaw).
Differential used in E-rickshaw
2 control arms (I used Maruti Alto control arms)
Wheels and Tyres (I bought 12")
Batteries 48 V and 40-100 Amp(4 batteries of 12 Volt each will be the most feasible option in India): More Ampheres means more range.
Iron strip (flattened rod) to join pipe pieces (may skip it if you have faith in welding)
Iron angle (iron/steel) to make batteries house and seat.
Drill bits (HSS)
Nuts and bolts
Paint: if you want to paint it
Tools: Cutter, Drill machine, Hammer, Welding machine(I outsourced this part), Rinches

Step 1: Arranging Parts for Making the Frame

I first removed rusting using twisted cup brush with marble cutter.
Cut square pipe into four pieces to make a rectangular shape with width equal to the width of axle (differential).
Then my kids painted these pieces.
Cut the square pipe for making the neck and keeping its length sufficient for the front wheels to steer.

Step 2: Frame: Rear Suspension and Joining/welding Frame

Weld these 4 pieces to make a perfect rectangle, ensure that both diagonals are equal. Be highly cautious at this stem because a wrong frame will not be good for your car.
(optional) I have an iron sheet, I cut triangular shapes from this and made holes in it to bolt it at all four corners of my rectangular shaped structure to be safe from welding failures.
Install wheel and tyres to the differential/axle.
Join leaf sprint to the differential. A bottom plate (along with bolt and nuts) will be required for this, i cut it from the iron sheet and make holes in it. However you may get it from market. I didn't find it in my local market and have to make it myself. Here my daughter is bolting it.
Now attach frame to the differential via leaf springs to provide suspension.
You may use leaf spring shackle to join, In my case cut it from the iron sheet and gave it desired shape (outsourced this part to an iron smith) who moulded it as per my requirements.
Finally the frame with rear suspension is ready and you may see it in the photo with my mother and kids.

Step 3: Front Suspension

It was the hardest part for me to design. My frame size didn't resemble with any cars in the market so I can't just buy parts and assemble them to make it work. I took a long time to design it and finally did it to satisfaction.

Attach the neck part to the frame (that we made in step 1), using the flattened iron rod after cutting and bending it as per requirement. Install the leaf springs to the axle (differential). Refer photos for clarity.
Now we need to add control arms and wheels will be attached to these control arms.
On one end there is a ball joint attached to control arm, I removed it first tried using hammer but finally has to cut it using iron cutter and then it was removed easily.
Install both two control arms on both sides of neck. We shall attach shock absorbers to these arms.
Weld an iron angle with a flattened iron rod and attach the shock absorbers on both sides as shown in photo. finally I attached 4 shock absorbers, 2 on both sides after I tested it for the first time. So weld angle in between control rods and not the way I welded it to make it better.
My photos are a little messy, please pardon me for the same. I was not having this in mind (that I will upload it to instructables) while designing and building the car.

Step 4: Battery House, Connect Batteries to Electric Motor/Controller

Now we need to place batteries somewhere:-

Cut one axis of L- shape iron angle to approx 90 degrees after marking as per the height/width of battery and frame so that the angle may be bent. Bent it to make rectangle and bolt/weld it with the car frame. In my case I have to make two rectangular cases for mounting batteries.
Now connect batteries if you have than one. In my case there were 4 batteries of 12 V/42A each. Motor is rated 48 V, so the input to motor must be 48 V. connect the batteries in series to make output of 48V and 42 Amp.
Put the batteries on the cabin created for them.
Now make connections of controller and motor as per the instruction manual of the motor and controller that you bought. I my case no manual was provided s I took help from videos of you tube.
Connect accelerator and test your battery, motor and controller connections. If everything seems okay install motor, battery and controller.

Step 5: Steering

Its the second difficult part for me after front suspension.

The steering wheel I bought from automobile market in Delhi (India) near Kashmere gate for approx Rs. 1100. The same was prices Rs.3500 on Amazon.in.
I bought second hand steering assembly (of Maruti) from local mechanic and connected it to the steering wheel.
Bolted two pipes to support steering wheel after drilling holes.
I used a self made clamp for drilling holes in parts simultaneously which is visible here in one of the photo. It proved one of the most useful tools for me.
Then I have to cut two pieces of flattened iron rod/bar to fit steering on it.
Bolt the steering after drilling holes at the required places in the bars.
Earlier I bought hand accelerator, thinking that I would convert it to paddle accelerator some how. But finally I bought one paddle accelerator.
For making seats I just welded iron (L-shaped) and placed/fixed wood planks.

Now my kids are enjoying it. We (4 kids and me) can easily sit on it and all kids enjoy it a lot. Although I spent approx. Rs. 60 K on it but I am happy with it. Thanks all for reading.