Swimming lessons aren't probably essential, but they are fun and great exercise. I was in swimming lessons from the age of 5 until 12. I always really enjoyed them. If you don't take your kids swimming that much or they don't enjoy it at all, then I wouldn't push it and try and explain to your in-laws that it's just not something you see as important. Hopefully it won't cause a huge wedge, but you are the mother and you do what's right for your family, not what someone else thinks is right. I plan to put my kids in swimming lessons, but that's me. I had a great experience with swimming lessons. And it is great exercise for healthy kids, especially in the winter when you don't get outside much to play. But ultimately, you need to make the decision for your family.