Hello Mukta,
Welcome to IL.
You must be so excited to travel to Bonn,Germany [ in case you haven't been earlier here] and explore the place.
Wow twins..I am sure they keep you busy

and I am glad that you found time to search this site and post your query in the relevant forum.I am sure someone from Bonn would be able to respond to your queries and provide information on the requested toddler groups.
Hope you have a nice time in Bonn and would love to hear from you about your travel experience and tips/suggestions to someone who is moving to Bonn.
Enjoy and hope to see you more in IL.