How do you get that inner child back?

I’m 27 and I’ve got a few kids, but I don’t know how to play with them. I had a very serious childhood, had to grow up fast and honestly any childlike wonder was beat out of me by the time I was a teenager. That was a lifetime ago and I’ve managed to make a somewhat successful life for myself but I notice I’m not good at playing with my children. I have no imagination, no childish hobbies or anything. I’ve turned into a very serious adult and I just want to be a fun dad. My wife is very playful and still has a lot of that inner kid but I’m just so different. Any other guys deal with this? Have any advice?