Because a + il contracts to al in standard Italian.
So:
This kind of contraction is very common in Italian.
Il is the masculine singular definite article, meaning the.
So:
Italian uses articles very regularly, often more regularly than English. In a simple descriptive sentence like this, using il with both nouns is completely normal.
If you wanted a diaper and a bib, you could say:
They come from a suffix that often has a diminutive sense, yes, but in these words you should treat them as the normal everyday nouns.
So in practice:
A learner should not automatically translate them as little diaper or little bib.
Yes. Vicino a and accanto a can both express closeness.
A rough difference is:
In many basic contexts, either one works, but accanto a often sounds a bit more specifically beside.
Yes, but the basic sentence order here is the most neutral:
You could also say:
That version puts more focus on the location first. Italian allows more flexibility than English, but the original sentence is the simplest and most straightforward.
A helpful approximate pronunciation is:
The stressed syllable is gli:
Depending on how detailed your pronunciation study is, you may learn that Italian gli can make a special sound that does not match normal English exactly. For a beginner, aiming for something close to lyee is a good start.