Blanketi la mtoto ni jepesi, lakini linampa joto vizuri.

It’s being treated as Class 5/6 (JI/MA). You can see this from:

• la (Class 5 possessive concord) in blanketi la mtoto
• li- (Class 5 subject prefix) in linampa
• jepesi (Class 5 adjective form)

Note: Many loanwords like blanketi can also be used in Class 9/10 (N class). In that case, you would typically see: Blanketi ya mtoto ni nyepesi, lakini inampa joto vizuri. Both patterns occur; just be consistent within a sentence.

Because the noun blanketi is being handled as Class 5 in this sentence. The possessive particle -a takes a class agreement prefix:

• Class 5 (JI/MA singular): la
• Class 9/10 (N class): ya

So with Class 5 agreement, blanketi la mtoto means “the child’s blanket.”

Adjectives agree with the noun class. For the adjective “light (in weight)” (-epesi):

• Class 5 singular: jepesi
• Class 6 plural: mepesi
• Class 9/10 (N class): nyepesi
• Class 1/2 (M-WA): mwepesi / wepesi
• Class 7/8 (KI-VI): chepesi / vyepesi

Since blanketi is Class 5 here, jepesi is used. If you made it N class instead, it would be nyepesi.

It’s built from several parts:

• li- = Class 5 subject prefix (“it” for a Class 5 noun like blanketi)
• -na- = present/habitual tense marker
• -m- = object marker for Class 1 (him/her, i.e., the child)
• -pa = verb root of kupa (to give)

So li-na-m-pa → linampa = “it gives him/her.”

Yes. -patia means “to provide/supply (someone) with.”

• linampa joto = “it gives him/her warmth”
• linampatia joto = “it provides him/her with warmth” (a bit more formal or explicit)

Both are natural.

• joto = heat/warmth (the sensation or quality)
• moto = fire or “hot” (as an adjective)

A blanket gives joto (warmth), not moto (fire). So linampa joto is the idiomatic choice.

Yes, common options:

• Without object marker: Blanketi la mtoto linampa mtoto joto vizuri.
• With object marker (very common for definite/animate recipients): Blanketi la mtoto linampa mtoto joto vizuri. Using both the object marker and the noun (“doubling”) is widely used in everyday Swahili when the object is specific or topical, though some grammars prefer avoiding unnecessary doubling. In speech, the doubled version is very common and natural.

Use the negative present with the Class 5 subject prefix and replace final -a with -i:

• halimpi joto = “it doesn’t give him/her warmth” So: Blanketi la mtoto ni jepesi, lakini halimpi joto.
  You can keep vizuri if you want to negate just the effectiveness: lakini halimpi joto vizuri.

Yes. You can place lakini at the start of the second clause as shown, or connect more tightly:

• Blanketi la mtoto ni jepesi lakini linampa joto vizuri.
• Or, more formal: Blanketi la mtoto ni jepesi; hata hivyo, linampa joto vizuri.

You need to change all agreement targets:

• Possessive: ya mtoto (not la mtoto)
• Adjective: nyepesi (not jepesi)
• Subject prefix on the verb: i- (not li-) Full N-class version: Blanketi ya mtoto ni nyepesi, lakini inampa joto vizuri.

Common alternatives:

• linampatia joto la kutosha (it gives him/her enough warmth)
• linamfanya awe na joto (it makes him/her have warmth)
• linamfanya ajisikie joto (it makes him/her feel warm)
• More colloquial/short: linampasha joto (it warms him/her up)