Wtih L'Open Tour you can buy a ticket valid for 2 or 3 consecutive days and take the bus and boat as you please. You can plan your routes as you wish.
With such a system you can enjoy the views of the monuments and the Seine from the rear terraces of the boats and the top decks of the buses.
When our kids were between 6 and 12 year they loved the hop on - hop off system. And we as a parent became more aware of the city plan.
The nearest hop-on is at Opera, where the different routes come together.