Quoting Brandi Coughlan:" <blockquote><b>Quoting B♥Z:</b>" DD is 3.5 Twice a week she has 1.5 hours of ... [snip!] ... & play too much so he pretty much watches tv all day bc he doesn't really have a good attention span to do coloring & stuff.."
There are some boys in my DD's gymnastics class and they seem to have fun! At this age, it's not a bunch of real gymnastics stuff. It's a lot of little fun activities.
Have you looked to see if there are any local indoor play gyms? Like here, there's a huge inflatable jump place. It's $8 to get in and you can stay as long as you want. DD loves it!