。
She's wholeheartedly devoted to her children.
Literal
She [topic-は] children [matters of-のこと] [target-に] is-devoting-self-wholeheartedly.
専心する ('devote oneself, give one's whole heart to') is the sister verb of 専念する: where 専念 builds on 専 + 念 ('exclusive thought / focus'), 専心 builds on 専 + 心 ('exclusive heart'), shading the devotion toward emotional wholeheartedness rather than pure concentration. Both are slightly literary. The progressive ~ている marks the state as ongoing and committed, fitting for a description of long-term parental dedication.