At the end of the day you need to do what is best for you. Just like, at their wedding, they need to do what is best for them. I can totally understand them wanting their wedding to be child free if they know a lot of people with children. I went to a wedding last year that was child free, and while the couple love and ADORE children, there would have been so many of so many ages (the groom has a huge family not to mention all the friends with kids) and it would have been very disruptive to their big day. The only exception was one of the bridesmaids who had a 4 week old baby, but the baby was kept inside the house (my friend had the wedding at her parents property) and she kept going inside to feed and check the baby was ok (bridesmaids mother was there looking after the baby inside the whole time).

Not saying you are doing right or wrong by going/not going, because the right decision is whatever you and your husband are most comfortable with. But just as you were hoping they would see it from your perspective, you need to see it from theirs. This is their big day. They only get this one day and want it to go a particular way. They can't make everyone happy so they need to do what is best for them and this is something they have decided to do.