How do you ensure that junior employees contribute their ideas?

Thanks a lot for this question!
I indeed believe that it is crucial that all team members are voicing their opinions and therefore contribute to a higher quality of the solution which we deliver.
At Roland Berger, we often work with structured brainstorming sessions which involve all team members - also in a virtual setting. In addition, we make sure that tasks are split and allocated clearly to the team members such that everyone is working - already on a junior level - on independent work packages. Finally, we have a very open feedback culture which allows to detect early if someone in the team does not feel that he or she can contribute adequately to the debate (e.g. bi-weekly feedback sessions, team barometers and bottom-up assessments for project managers).
I hope this helps - feel free to reach out in case you need more information