We didn't start swimming lessons until just before DD1 turned three. She wouldn't put her head under at the first lesson but next lesson she was swimming! She was moved up after two lessons to the proper swimming class. I'm not boasting about how good she is at swimming. I'm just pointing out that if you don't have the chanceto get them into swimming lessons until later its not the end of the world. I believe it's important to get them used to water but I've also found that my DD2 is over confident now in the water. She's just turned two. Sure she can swim to the side but I'm not hugely confident she could save herself if she fell in the water. She's more likely now, after having swimming lessons, to jump in the water without us watching which scares me to no end! I wouldn't worry too much if you do delay the lessons until after winter. My girls haven't got sick from swimming and I don't think the risk is any greater than going anywhere else that has a lot of people in the one place eg shopping centre. But he's still young and with your DH, maybe it's better to wait that little bit longer?