Dear @Jj061987,
You can send your child to a Kinderkrippe as soon as you feel it is suitable for your child to do so.
There is no specific rule such as 'you should register your child 6 months before you need a place'. The procedures for getting a place in a Krippe or Kita will vary slightly throughout Germany and the length of time depends on capactiy and demand. Generally it is advisable to research which Kitas are nearby and to make enquiries as to whether they have any spaces free, ask to visit the Kita etc. The part of Germany you are in may also have an online portal to search for free places.
The Jugendamt has offices in all parts of Germany and are responsible for assisting inidivduals who are having difficulty finding a Kita place. There are also migrant advisory services throughout Germany which can help with this.
Best,
Éanna