Everyone seems to have different thoughts about when you should tell your kids the truth about Santa Claus, or if you should even encourage the idea of Santa with your kids in the first place. However, at ages seven and four, my kids still believe in Santa, and I think it's great.
Childhood is magic. My kids have had a less-than-perfect life so far, and I want to make things as fun as I can for them, especially around the holidays. The fun parts of Santa – a jolly, friendly, caring person who flies around the world on a sleigh pulled by reindeer and gives presents to everyone – is, well, fun, and I want my kids to have as much fun as they can. However, we are a blended family. My step-kids (a 10-year-old and a 6-year-old) were never taught about Santa Claus, and we have to actively work to prevent them from ruining things for the other kids who believe in Santa, both at home and at school. It's not easy.
As for whether or not it's OK to "lie" to our kids about what's real, we actually do this all of the time – from the first game of peek-a-boo to telling them dragons are a thing. Kids need to learn how the world works in an age-appropriate way and on their own. I think it's OK for kids to learn the truth organically, or to use their own reasoning ability to answer the question, "Is Santa Claus real?" when I respond with the question, "What do you think?"
The holidays are hard enough for kids and adults, without sapping what little fun there is out of them. I plan to support my kids no matter what they believe, and have made the choice not ruin it for them.