Based on your situation with a terrace house having disconnected front and back gardens, here are your options:

LawnMaster OcuMow 16 or 18 (Recommended)

These "drop and mow" robotic mowers would be ideal for your situation:

Perfect for disconnected lawns: Designed specifically for the scenario you described.
No perimeter wire needed: Uses vision-based navigation instead.
Simple operation: Simply place it on the front lawn, let it finish, then move it to the back lawn.
Obstacle avoidance: Built-in cameras detect and avoid toys and other obstacles.
Size suitability: Both models can handle your lawn sizes (front: 25m², back: 120m²).
Charging station: The OcuMow 18 comes with a charging station that can be placed on your larger back lawn, allowing it to automatically return and recharge itself.
Edge trimming limitation: You will need to do some manual edge trimming, as the edge cutting capability isn't as precise as the Yuka Mini.

Yuka Mini
While not specifically marketed as a "drop and mow" solution, the Yuka Mini could work:

Self-navigation capability: Can navigate from front to back itself if there's a navigable path.
Superior edge cutting: Provides better edge finishing than the OcuMow models.
Obstacle avoidance: Good detection system for toys and other items.
Compact size: Well-suited for smaller spaces like your front lawn.
WiFi connectivity: Works with your existing network in both gardens.
Limitation: You would need to manually move it between gardens. The mowers lift sensor will be activated each time and need to be cleared as this is not designed to be picked up and moved between lawn.

Recommendation

The LawnMaster OcuMow 18 would be your best option since it's specifically designed for disconnected lawns with a "drop and mow" approach. The charging station can be placed in your larger back garden, and the obstacle avoidance feature addresses your concern about children's toys. Just be prepared to do some edge trimming to achieve a perfectly manicured look.

https://easylawnmowing.co.uk/exploring-drop-and-mow-feature-lawnmaster-ocumow-18/
https://easylawnmowing.co.uk/lawnmaster-vbrm18amdr-ocumow-review/

Thanks
Mark