My pet mouse had babies, and their numbers multiplied rapidly.
My pet mouse have birth to babies, and their numbers kept increasing rapidly.
ご質問ありがとうございます。
・「My pet mouse had babies, and their numbers multiplied rapidly.」
「My pet mouse have birth to babies, and their numbers kept increasing rapidly.」
（意味)飼っていたネズミが赤ちゃんを産んで、どんどん数が[増えて](https://eikaiwa.dmm.com/uknow/questions/8845/)しまった。
<例文>My pet mouse had babies, and their numbers multiplied rapidly. They're all very cute though.
<訳>飼っていたネズミが赤ちゃんを産んで、どんどん数が増えてしまった。 みんなとても可愛いけどね。
参考になれば幸いです。
アメリカ合衆国 
