Sorry but the day is not about only the bride. It is the joining of two families. Not Bride on Parade day. I have to be honest that I wouldn't even look for a babysitter if it was my sister. I would not go. If it was a friend or other relative then no problem, but my sibling no way. Sorry but I would be very hurt and insulted.
MTE.
they will be involved, they can go to the ceremony just not the reception. My brother is getting married in May, they have his reception to look forward to.
And they will. You have the right to have anyone you choose come to your wedding but you don't seem to respect that others have their own priorities. There were a lot of hard feelings when my nephew got married. His Bride and her Mother planned one humdinger of a wedding, It was "perfect". The perfect dress, the perfect reception, the right flowers, and it cost close to $100,000. Yup....it was perfect all right.
His sister married several years earlier. It was lovely. Not perfect. My brother and DSIL gave her a beautiful wedding, invited whoever she chose and kept the drama to a minimum. The way our family interacts with my niece and her Dh is way different than the way we all interact with my nephew and his DW. I love my nephew and like his wife but it is not the same anymore. Not so with his sister. You see, it was not who was or was not invited to their weddings that was the issue, it was the attitudes that they displayed throughout the process. One behaved as though her wedding was a family event and while she was certainly the showstopper she understood that she needed to respect the people who have been in her life. That did not mean they all needed to be included in the planning or that small childen were automatically invited. It meant that she wsa upfront about the wedding she wanted and allowed people to make their coices depending on their own circumstancews.
Now her brother's Bride was the opposite. This day was totally about the Bride. And she was stunning. I still cannot get past the disrespect shown to my brother and my wonderful sister-in-law. We all did enjoy the wedding but no meal will compensate for all the tears those two caused my nephews family. Was it worth it? I have no idea but IMO, of the two weddings I look back on Amy's with a warm feeling and with Brians....

. It was okay but the turmoil took so much away form the day for me an for those of us close to my brother adn his family.
OP- you do what you want, it is your wedding and the children can and will enjoy their uncle's day. I don;t know how old they are but if this is the hill you want to die on, go for it.