I was bridesmaid twice when dd was v little. Once at 4mo and again at 5mo.
The first time, the bride had a baby 5 weeks older than dd but we both did things differently. She expressed enough for the day and her family fed her ds. Dd is a bottle refuser so I kept sneaking off to a side room to feed her as I had to pull dress right down to feed her. I sat on top table and tbh DP spent most of time pushing her round the grounds, rather than sitting at his table with her.
We (dp, dd & I) stayed with bride, the night before, as huge house, 5hr drive & she insisted as it would save us money. I couldn't have left dd overnight for two nights (still haven't left her overnight, at all and she's 10mo).
For the second wedding, the plan was for us to drive down (2hr drive) on morning of wedding, despite other bridesmaids staying in hotel with the bride, the night before. I knew before dd was here that I didn't want the pressure of working round bf, overnight. Dd was supposed to spend day with DP's sister and we'd drive home in early eve.
That all went pearshaped when dd decided she hated the bottle. We ended up taking dd (to a childfree wedding). The bride was brilliant about it. I'd arranged with one of the other bridesmaids, that DP & dd would spend day around and about the venue and I'd use her room to feed/change dd, before I told the bride that dd would have to come. The bride said not to be daft and had a place set for dd, at our table. I just snuck off to feed her, as dress again, needed pulling right down.
Didn't mean that to be so long, but wanted to show different approaches and that plans can easily go out of the window.