We started going when C was 6wks adjusted. I just took him in in his capsule. If he was awake I would lay him on the mat in front of me (just on a muslin) otherwise I let him sleep. There was a big range of ages in the babies, some mums had crawlers/toddlers and it looked much harder!!! Our teacher was great and gave lots of examples/modifications for including baby in the poses if we wanted to.
If C needed feeding I would just feed him there. Sometimes he would be needing to go back to sleep just before the end of the class so I would let him go to sleep on me and just relax for the rest of the class or the teacher would hold him for a bit so I could do some more.
We stopped going when C was around 5mo or so as it clashed with his nap time and then later with lunch time.
TBH some days I didn't get much out of the yoga itself but it WAS a great way to get us both out of the house and interacting with different people again