When Alice was about 6 months old, we brought her one of those seats to put in the bath so that she could sit up and splash! We loved it, she loved it. But recently she had been struggling to get in and out of it properly and looked a bit restricted as if she was desperate to move about more. She we took it out and put her in the bath. Disaster!
She screamed and screamed and wouldn't sit in the bath without it. I realised that it had become a comfort to her and that she didn't feel safe without it. So for the past week I have been very gently encouraging her to take a bath without it. I went completely cold turkey on her and removed the seat completely. The first night, we had hardly any water in the bath. The second night we added more but I leant right over and held her to make her feel safe. Now, after a whole week of this, Alice is taking baths happily without the seat.
If you are using a bath seat, be warned! I know they are absolutely amazing, but as soon as your baby can actually sit properly unaided or move about more, it might be an idea to think about getting rid of it. In hindsight, I would have definitely gotten rid of ours sooner to save Alice a week of distress!