the same thing happened to me at my cousins wedding...Ds was fully bf and all of my family was at the wedding so I didnt have a babysitter anyway..i just rang the bride and she said it would be fine...they didnt want kids there as the church part was important and they didnt want screaming kids around...not that any of the kids screamed. Ds was soo quiet you wouldnt have evcen known he was there and he slept the longest he ever had at the reception so it didnt matter.

If you dont feel comfortable going then dont i am sure the family would understand..plus 4 months is still a tiny bubba aho needs his mummy

Good luck hun xx