I decided to send dd to a German speaking kiga so she would have learnt German well after 3 years, ready for school since it looked like we might be staying longer term.
I know families whose dc have been at bilingual kigas. They keep their English up best in a purely Engish speaking kiga. Tbh if I had another dc in Germany, I wouldl ook for a purely English language Montessori kiga. Dp have told me that in those bilingual kigas, the dc overwhelmingly speak German together anyway, so I'm not sure they are worth it for people who speak English at home.
If you have a choice, certainly go and look at them. Might be nice for you and ds to meet English speaking friends so you can keep his English up later if he is to attend a German speaking school.
I think on the whole, German kigas are ok, they differ from a British nursery in many ways, not all bad. For instance the carers are not university trained, they are people who have gone through the lower sorts of German school and then done some training. They manage big groups, generally the groups are of mixed ages 3-6 all together. They are also quite cheap in comparison. I have read some things on MN about the TV being on in nurseries and so on and I really think you can comfortably say, this is never going to happen in a German kiga.
Ours had nice meals, freshly cooked and not those awful big kitchens delivering rubbery, mass produced gunk (which is what happens in schools) this depends on the kiga though.
Mine were from 9-3pm. They were quite strict about dp picking them up either straight after lunch or at 3pm (not inbetween because it would disrupt nap time - which I think is fine). The day began (mind you I had 3 altogether) with sitting down and singing songs, then pottering about indoors, doing what they wanted. They stop for a snack (which you have packed) and then weather permitting play outdoors doing what they want, digging in the sandpit, climbing frames, they had a nice wooden castle, things to hide in and a shed full of bikes, tricycles, and carts and things they could help themselves to.
Then inside again to wash hands, have lunch together, everyone brushes their teeth together, gets changed, lies down and has a nap. Everyone gets up together, gets dressed and goes to play outdoors till the parents come for them. I don't know what the bigger dc do who no longer nap when the weather is bad and they have to stay indoors, something quiet I presume. I know my dd was into "helping the cook" who was thankfully a lovely Croatian granny who was fine with that. I am sure she was totally in the way.
In some places, the dp are friendlier or have more time to chat than in others. I think it's nice forthe dc to make friends like that and in Germany they mostly just go on to the local school, so unless people move away, there is continuity of friendships there.
The Catholic kigas my dd attended were just lovely, unlike the school which was a real disaster. She went to 2 x Catholic kigas which I both found great, lovely people and 1 other one when we moved inbetween which was the rule-based horrible one , I moved her out of.