Are toddler activities like swimming, music, art etc really necessary?

You (or your child) shouldn't allow activities to feel like a chore. If you can find a fun activity that is physically engaging your toddler then by al means please do. Toddlers need at least 2 hours of physical activity a day! It helps with their coordination, muscle growth and bone density. If spending money on classes is an issue, consider taking your children to the park or something more frugal. You are absolutely correct in saying swimming is a great activity for children. It sounds like you've picked a great activity for you and your children. If you're curious about the importance and benefits of active play for your kids check out this link: http://www.kidspot.com.au/Toddler-Development-The-importance-of-active-play-for-toddlers+6069+26+article.htm