Could you please fold up your stroller because there are too many people here?
Could I ask you to collapse your baby carriage because it's so crowded here?
どちらも「とても混雑しているのでベビーカーをたたんでもらえますか？」という言い方です。
1) Could you please fold up your stroller because there are too many people here?
2) Could I ask you to collapse your baby carriage because it's so crowded here?
「ベビーカー」は stroller や baby carriage と言います。
「（ベビーカーを）たたむ」は fold up や collapse が使えます。
ご参考になれば幸いです！
日本 
