A couple of generations ago "adult language" was fairly uncommon--at least in common social gatherings, particularly ones that included children. Using an explitive had a LOT more impact when it was a rarely used word.
You cannot dictate what others allow in their home; you can protest, but it is ultimately up to them to decide what they will allow and enforce or not. However, in you rown home YOU are the ones who decide. My recommendation is to start doing more of the hosting, and let all the guests who tend to use bad language know that it is not allowed in your home. If they use bad language, depending on the specific circumstances, you may choose to remind them, giving them another chance, or to evict them.
When you attend family gatherings at others' homes, let them know that if bad language is used, you and your family will be leaving and not returning.
The disrespect shown by not respecting your wishes concerning language near your young children is reason enough to sever ties. IMO, you have been overly generous.