1BHKs cannot magically convert themselves into 2BHKs, especially if you want to keep the H aspect of the flat (the hall). However, it is understandable that sometimes there is the need for more for say, a growing family, and this requires more leg space.
To achieve this leg space, you can move the kitchen in your house. Many newly built homes have areas like pantries, and this is where you can shift the kitchen to should the need come to it.
You can also move your wash basin inside the bathroom to use the wash basin area as a kitchen platform.
This space will be small, just enough for a platform, and you will have to keep utensils elsewhere.
This may decrease your kitchen’s size, but gives you another room to utilise, and even if it’s a small room, it may be enough for a baby for that time being. Places like Mumbai where real estate is small have people using balconies for kitchens.
If you are at the right ground level in an open area, perhaps you can do it too (but consider this option severely before taking it up.)