If you don't have to send your kids to day care, then why would you?
There are plenty of ways kids can interact with other kids, when they're developmentally ready for it (and 3.5 is normally when children are starting to play 'with' instead of 'around' other kids). There are so many playgroups around it's not funny. There are kids gym classes, dance classes, swimming, etc.
I sent DS to childcare because of uni, and never bothered with 3yo kinder because of the activities he had during the week on top of childcare 2 days a week. I kept sending him to childcare when I was on leave from uni because I ended up needing the break to be with DD, not for his own benefit (because, given a choice, he would have stayed home and, in a perfect world, I would have kept him with me).
Childcare is increasingly being marketed as 'early education', but it's not, really. They use developmental ideas to create the care environment, and it's stuff that an engaged parent can do at home. There are many reasons a lot of mums can't engage with their toddlers - older and younger children, work, study, personal illness etc - so this isn't a judgment call, it's just the way it is. It's the way it was with me. I think I'm one of those mothers whose cracks really show when I'm not supported, and childcare helped me out when my parents moved away and MiL took a step back when we were living with her (instead of being the extra hand I was under the impression she'd be).
Now I need childcare for DD for the next 4 or 5 months till end of academic year. After that I don't want her in care. It's only because I need it to study. She doesn't need it for socialisation - she mixes with kids at her brother's activities, cos she comes with me!
I also find that people who fall back on "it's great for socialisation" are afraid to say they need the break. I'm not - I needed the break!
Believe me, if you're loving being at home with your child, then your child doesn't need day care, and that's a good thing