Hi, I'll visit Bonn on June for 4 days with my two boys. One is 5,5 years old and the other one is just 10 months. We'll stay at Hilton by the river. What would you reccommend? What's a must see?

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The chocolate museum in Cologne comes to mind, maybe the "Deutsches Museum". I don't know what else there is for kids, the other museums are mostly for grown ups, like the "Bundeskunsthalle", the "Haus der Geschichte", etc.

Don't be dissapointed, the Hilton Bonn is ugly and has no allure at all, my mom stayed there a few weeks ago, so I had the opportunity to check it out, it reminded me of all the Ibis Hotels that I stayed in when I was working before going to the university.

In Bonn: Watching the ships on the Rhine from the promenade walk or from the lookout next to the Schloss, where you'll find two real old cannons

The zoo in Cologne

Cologne cathedral is bound to impress even littlies

A boat ride on the Rhine. Since I don't think you'll want to take a long day trip by train and boat with the littlies, the most spectacular part of the Rhine gorge South of Koblenz is out. However, the valley right South of Bonn is quite pretty with the Seven Mountains, the islands and a couple of castles. Do the boat ride from Bonn to Linz and back, which will take about an hour in each direction. Go for a short walk in the little town, have a coffee resp. ice-cream and then go back.

Go up the Drachenfels, the steepest rock with the castle ruin on top next to the Rhine. No need to walk all the way up, there is a cogwheel train:
Drachenfelsbahn

The Sealife aquarium in K�nigswinter

All these can be done by public transport.
If you have a car, there will be even more options.