Do UWA lenses and street photography go well together?
(Dis)advantages of UWA lenses:
Most people try to not use UWA (ultra-wide angle) lenses for portraits. Faces do not go well with UWA lenses - especially if they are not in the middle of the frame, and thus will be distorted. It is by no means a hard rule to not use UWA lenses for portraits - but most people will find the effect very unpleasing.
Also, with UWA, you have very limited options regarding DOF (depth of field) - it would be hard in your composition, anyway (because of the distance between the subjects), but since everything is in focus, I have nothing to guide me. f/8, as you have used, seems to be overkill - you might already run into diffraction softness here, and since f/8 will offer its hyperfocal distance at 76.7 cm focus distance (and from looking it seems that your focus distance is around that value), almost everything will be in focus (except things extremely close to the lens - half of the hyperfocal distance minus the lens's length and the flange distance, so around 20cm).
In my opinion, in street photography, you do not need/want to have a picture that is sharp from end to end: a limited depth of field will help you to draw attention to the main act in the photo. With UWA, this tends to get really hard, as the hyperfocal distance falls shorter and shorter - even at wide-open apertures.
UWA lenses can give some spectacular insights - but they are not meant to be "always-on" lenses to spare you to walk away 2 metres to get everything in your framing. I think of UWA as a tool to give spectacular impressions of the wideness of space - take, for example, a large hall. But since your photo has no need for this sensation of space (as everything happens within 2 squaremetres), UWA might not be the best choice.
Regarding the composition of your photo:
It is difficult to explain why a picture has a certain effect to a viewer. It is especially difficult to find out if it is only oneself or everyone (without starting a poll, that is). I will try to elaborate it, but do note that everything here is 100% subjective.
The composition as a whole feels like you wanted to photograph the sleeping boy, but then you found that including his mother and sister would be a good idea - and recomposed a bit. It looks like a technical approach to a picture - i.e. using someone's guidelines as a rule of fact that works every time. The angle is top-down, which also looks to me as if you did a sort of a compromise here. UWA is bad for compromises in my experience.
Also, this top-down approach makes it hard to see where I should look. My look path was:
boy's shoulder - boy's head - blanket - shoulder - mother - tree - mother - sister - street. I would try to get (close to) level, maybe even a bottom-up angle with a bit of street in front.
To me, the image lacks some sort of "context" - to see that they are living on the street, I have to look behind the boy and behind his mother.
I think that it looks to me like a technical approach because I used to do the same thing, too: Take a rule-of-thumb and use it as a hard rule, then refine it by learning its limits and potential. I certainly have a lot of similar photos in my gallery, and with increasing routine, they become less and less (that is not to say that I do not take bad (UWA) shots today!).
The particular eye-catcher in your photo is that you used a portrait (vertical) framing - again, no hard rule, but it adds to my impression that it is a compromise to get everything inside the frame.
As @Arvo pointed out in the comments, cropping the lower portion of your photo (i.e. the blanket) certainly helps. UWA photos benefit from cropping more often than other photos (in my personal experience).
What I would have tried:
(with unlimited lenses and without knowing the limitations of the scene)
Go for a 35mm or 50mm wide open, toddler in front, boy at the far end, in a wider angle (as in: compose the subjects from left to right, not in a straight line and behind each other). This way, the smallest subject is in the front and the largest (by appearance) is in the back - it might also get you some impression of movement, with the toddler in front.
Or use the UWA lens, position the cam almost exactly over the mother, and shoot (almost) straight into the ground. This could, in theory, play the advantage of space to get a feeling of alienation.
Again, please note that I do not know what the scene there looked like, how they would have reacted, how much time you had, what lenses you had at hand,... - I did so many bad photos (and still do them) that "I would have made it better" would be an outright lie. Do not take any of this as "your photos are bad and you should feel bad!"