How frequently my children call is not something that I keep track of but I would say both Son and Daughter call at least a couple of times a week.
Son calls around to mine maybe a couple of times a week as quite a lot of his ‘stuff’ is still here, mainly paperwork, a lot of which is still delivered here and one of his vintage cars in my garage and his caravan parked on my drive. Luckily, it has room for several cars, so I don’t complain.
Daughter and family live literally across the road, so I tend to wander over whenever I feel like it.
All my family have a key to my house, including Grandchildren and I have keys for my Daughter's house but not my Sons.
No one needs to call if they are coming round, just let themselves in, Son usually rummages in fridge before saying hello.