my baby cried when he(she) first ate solid foods because his(her) stomach wasn't used to it and it was difficult to digest
eating solid foods for the first time made my baby cry because his(her) stomach wasn't used to digesting it
「赤ちゃんが離乳食を始めて、胃が慣れていないので、消化できずにお腹が痛くて泣くようになった」＝ my baby cried when he(she) first ate solid foods because his(her) stomach wasn't used to it and it was difficult to digest / eating solid foods for the first time made my baby cry because his(her) stomach wasn't used to digesting it
ボキャブラリー
離乳食 ＝solid foods/solids/first baby food
胃 ＝ stomach
消化する ＝ digest
慣れていない ＝ not used to ～
泣く ＝ cry
イギリス 
