I'd go to Megan's Bay, very calm and shallow, no drop offs and good food bath room options.
I will be there with DW week of 3/11 sailing. No kids but I'd take me 2 1/2 Yr old grandson for sure. Take a taxi and just let them know when you want to go back.
You can/should bring your own swim support wear for the children
Have fun 🙂