Since infants can't speak, they cry and scream until they get what they want.
Literal
Infant [topic-は] speak [nominalizer-こと] [subject-が] do-cannot [because-ので], want [attributive-の] thing [subject-が] hand [in-に] enter [until-まで] cry-scream.
A complex multi-clause sentence. ~ことができる is the formal potential. 手に入る ('come into one's hand / be obtained') is a fixed expression for acquisition. 泣き叫ぶ is a compound verb 泣く ('cry') + 叫ぶ ('shout'). まで marks the endpoint of continued action.