What can "little silver jet" mean in this sentence, as something that interested a baby when it "fell to the ground"?

Question

The sentence I'm talking about (in bold), along with relevant context:

She was eight years old and small for her age, and the baby brother she carried on her left hip was large and plump [...] He was holding a biscuit in one hand and a bright red plastic spoon in the other; while the top part of his little body was well protected by a vest, shirt, coat and an over-sized bib, the bottom part was bare. Round the ankle of one leg was a little silver anklet with two bells.

[...] The little silver jet that arched and fell to the ground delighted the baby, who made an attempt to touch it, and the girl, who had been scolded by her mother on several occasions for not taking care of her baby brother so that he sat in his own puddle and splashed in it, now said sternly "Tee Tee, you dirty boy, leave it alone!".

— "Big Sister" in Or Else, the Lightning God

The sentence seems unnecessarily long and convulated to me. Too much information crammed into one single sentence. But I more or less understand the gist of it. Still, it would certainly be helpful if someone could break it down or simplify it.

What I'm not sure about is what "little silver jet" and "his own puddle" mean in this context and how they relate to each other. My overall understanding of the sentence (that is, what the writer is actually trying to say) is hazy at best. I suspect there's some baby vocabulary involved. Maybe words like only mothers or grown-ups use—which I'm naturally not very familiar with, being only 13.

Answer 1

My guess would be that the "little silver jet" was a stream of urine, given that the author helpfully informed us that his "bottom part was bare" and then refers to "his own puddle".

There's no baby terminology that you're missing here. The author is using intentionally opaque language in order to avoid being crude.

Answer 2

Carl Reinke's answer covers the specific terms asked about. But you also commented, requesting a break-down of the sentence. While asking additional questions in comments is generally not encouraged, a break-down is still on-topic for your original question, so I shall happily provide one.

Here, I break the long sentence into five shorter ones. Parts in italics have been added for clarity. Parts in (parentheses) specifically explain the two terms you asked about.

1. A little silver jet (a jet of liquid that caught the light and flashed silver) arched and fell to the ground.

2. The jet delighted the baby, who made an attempt to touch it.

3. The girl had been scolded by her mother on several occasions for not taking care of her baby brother.

4. On those occasions, as a result of her lack of care, he had sat in his own puddle (the puddle formed by his own urine) and splashed in it.

5. Wanting to do the right thing this time, the girl now said sternly "Tee Tee, you dirty boy, leave it alone!".

Answer 3

Breaking down the sentence

• The little silver jet
  (a stream of urine)

• that arched and fell to the ground
  (describing the trajectory of the urine stream)

• delighted the baby,
  (the baby enjoyed seeing it)

• who made an attempt to touch it,
  (he reached out and tried to touch the urine stream)

• and the girl,
  (meanwhile, his big sister who is taking care of him)

• who had been scolded by her mother
  (had been reprimanded in the past)

• on several occasions
  (many times)

• for not taking care of her baby brother
  (for neglecting the good care of her baby brother)

• so that he sat in his own puddle and splashed in it,
  (so that the baby ended up sitting in a puddle of his own urine, even splashing in it)

• now said sternly
  (the sister now said)

• "Tee Tee, you dirty boy, leave it alone!"
  (The sister tells the baby not to touch the urine, calling him a dirty boy for wanting to play with it.)

Explanation

The baby, who was unclothed from the waist down, urinated in a arcing stream. He enjoyed the look of the sparking stream of urine and reached out for it.

Their mother had scolded the sister many times for neglecting the baby. The sister had even left him sitting in puddles of his own urine, splashing his hands in it.

So now she scolded the baby, calling him a "dirty boy" and telling him to leave the urine alone.