Can anybody help me to find the origins of Spanish phonemes /ch/ and /j/ for
my Arabo-Romance project?

I know that /ch/ in many positions originates from consonant clusters *-ct-
like in noche < *nocte and *-lt- like in escuchar < *a(u)scultare. But how
do we get all those _chiquitas_ and _muchachos_?

As for /j/. I know it hides several Old Spanish phonemes: /S/, /Z/, /dZ/. I
can fugure somehow that in e.g. _dije_ it was /S/ comparing with Portuguese:
dije < *dixe ["diSe] < *dissi < *dixit. But what on earth made /L/ turn into
jota? What stages had the process? I'm comparing Sp. _ojo_ to Po. _olho_ and
VL _oclu_ and get lost in doubts...

Patiently waiting,