Who decided they were weeds?

I looked up at Dictionary.com the definition of a weed. This is what it said...

1.a valueless plant growing wild, esp. one that grows on cultivated ground to the exclusion or injury of the desired crop.
2.any undesirable or troublesome plant, esp. one that grows profusely where it is not wanted

My Little P spotted these a couple days ago when I was weeding the flower beds to get ready for spring. She was flabbergasted to see me rip these beautiful flowers out the ground. She almost seemed sad for the little plant and asked it she could save it. They are now appropriately placed in a mason jar in my kitchen windowsill.

When I saw a weed she saw a flower and I thought, WHO decided that dandelions are here by considered weeds? I have grass growing in the cracks of my sidewalk, is it now called a weed, or do you still call it grass?

Why do we say our children are "growing like weeds" I don't consider them valueless, more like priceless! Is it because we can't keep them small, they "grow profusely" even when we as parents aren't quite ready?

I guess I would prefer my babies were weeds, strong and hearty, growing profusely. I certainly am not interested in delicate flowers and wither at the first sign of distress.