。
I'm just not comfortable around children and babies — it's a visceral thing.
Literal
Children [and-や] babies [topic-は] physiologically uncomfortable [explanatory-なの].
生理的に苦手 ('physiologically uncomfortable with / can't handle on a physical level') pairs the adverb 生理的に ('physiologically / instinctively') with 苦手 ('bad at / uncomfortable with'). This combination is commonly used in modern Japanese to express a deep, bodily aversion rather than a rational dislike. The explanatory なの at the end is feminine casual — offering this as a personal confession or explanation.