In my childhood my teeth was white and later on i did not brush my teeth well and it became a yellowish white. is it my natural teeth?

Should be white: Your natural teeth are white. They become stained yellow with years of tinted food and drink and poor dental hygiene. These will return to white with proper dental care. Bleaching is optional.

Baby teeth are white: Baby teeth ("milk teeth") are usually very white. The adult teeth which follow have much more of the dentin (yellow or orange or gray) layer and so appear darker, especially at the gum line. Sounds normal.

Not uncommon: The longer you’ve had your teeth, the more chance you have to wear down their white protective coatings.The good news is a professional home whitening system with custom trays for the long term effect. You will be very happy with the results and white teeth again.

They're still white: ... but probably stained. You would be surprised at what a difference a professional cleaning bu a dentist and hygienist makes. After your teeth are cleaned and examined, you can discuss ways of whitening them if you want them even brighter. All the best....