Why do I need a website? Two words: Marketing and Credibility. Do you have a letterhead, business cards, or signage on your shop or office? In the 21st century, a website is just as, or even more important than all of those things.
Your potential customers who are searching for a product or service will look on the internet first, and then search the yellow pages, advertisements, or other information sources. Without a professional, well-written website, your business is virtually invisible, compared to your competition.
Does your business card or signage include an internet address? It could reflect poorly on your company if it doesn't.

Why don't I get my son/daughter to put one together for me? If you are confident that your son/daughter can effectively market your business then that is an excellent idea.
However, poorly built or unmaintained websites or even a well-designed website that is not properly marketed, is almost as effective as having no website at all. The website, like your business or storefront, must be properly advertised and be regularly submitted to search engines so that it will be in the top listings.
A company with a website which ..

has lots of "bling" but little solid information

does not enhance your business' credibility

takes forever to load

has all e-commerce and little or no information

is all articles and PR with no information about the products/services or people

is no longer functioning

.. tells the internet-savvy audience a lot about the company and its management.