Japanese sentence ending

I recently came across something that puzzled me.

Ani wa inu o kowa-garimasu.
(My big bro is scared of dogs.)

Kodomo ga atsugatte imasu.
(My child is feeling hot.)

In such cases when do we end off the "garu" form as ".....garimasu" and when to use it in the middle of a sentence as its 'te' form?

I also noticed such cases for other sentences with actions and adjectives too!

Thanks!

How about this?

Ani wa inu o kowagarimasu.
(My big bro is scared of dogs always.)
Ani wa inu o kowagatte imasu.
(My big bro is scared of that dog now.)

Kodomo ga atsugarimasu.
(My child feels hot always (when he wears that sweater.)
Kodomo ga atsugatte imasu.
(My child is feeling hot now.)

That helped a great deal, thanks :)