As you can see the first in the list looks like a bear cub so the answer is cub and the second looks like the sun so the answer is sun.
This was designed for young kids so the answer is not some esoteric foreign language import.
Please spoiler your guessed word.
WED. I think that’s a drawing of a bride.
wed?
I was going to go with wig, but I think it’s a bit of a stretch. But it’s the only noun I could think of that fits somewhat, assuming they are looking for a noun.
wut?
Is the real answer that the creator of the test meant to make it “nun,” but made an oopsie?
I think this is the most likely. I thought it was a nun.
WAC. That’s a welding mask pulled back on her head. She’s about to work on a B-52.
Wig
?
There are not very many three letter words beginning with w. I would have thought wed or wig. Maybe you could make a contrived case for wee, wid, woo, wow, who or why - I can see some merit to the last one in this context. 
You’d think wig would focus more on the hair and wed would involve more people and maybe a ring.
Hope I’m far enough down where I don’t have to add spoiler.
They definitely made a mistake, the word should have begun with an N, and the answer would be Nun.
The page is testing knowledge of the short ‘u’ sound, and only nun would fit that criteria and picture. Also, at that age the answer would be an easy noun.
My cite is 30-mumble years of teaching early childhood, and I’ve come across pages like this before.
My children would have never gotten Nun. If the dress was black and white? Maybe.
Very young, which this worksheet suggests its for? Never.
Yeah, I don’t think my 5 year old has even heard of nuns and I’m not sure what ages you’d expect to be familiar with them. These are simple words so I wouldn’t think it would be for much older kids.
If that hypothesis is correct, and the puzzle had been presented with an N, then I probably would have figured it out, but it might have taken a little time.
In other words, I would have needed a second to nun.
Or if the habit had Sally Field wings.
Nun of us iz as smart of all of us, wow. The figure does not particularly look like a nun either. No crosses or scolding.
And the level of handwriting skill shown here fits that age group as well. I think a kid of that age would have to be in a Catholic family, at the very least, in order to know what a nun is and what one looks like.
My favorite guess (found on anther site) is:
WTF
But “wed” is so much more common to be known at that age?
I wasn’t raised Roman Catholic but I certainly would have thought of “nun” before “wed”. That doesn’t look like a typical depiction of a wedding dress.
Also, all other answers are concrete nouns.
There’s no such thing as a “wed”. It’s an abstract state of existence.
If you’re advanced enough to get “cub” for a baby bear, you’re advanced enough to know what a “nun” looks like.
If you know what a nun looks like, including the black habit, be sure to tell the creator of this stupid quiz.