I wish you wouldn’t generalize like that. I have 3 daughters ages 5, 2 and 6 months and they’re anything but dumb.
The oldest one turns five in a month and she can already read and speaks 2 languages, they are all very intelligent. They may be a pain sometimes, selfish at times, but definitelly not dumb. In many cases kids are a reflection of who their parents are, so if you think your kid is dumb… look in the mirror.