The short answer
Yes, with a firm hold of hands. Children love the drummers, storytellers and acrobats, especially in the cooler early evening. The crowds are the main thing to manage. The snake charmers and the men with Barbary macaques expect payment for any photo, and many families prefer to watch them from a few metres away.
In more detail
The square is at its best for families from late afternoon, when the food stalls go up and the circles of performers form. Gnawa drummers, storytellers and acrobats draw rings of local families too, so you are rarely the only children in the crowd. The orange-juice carts are a reliable hit.
Crowds build quickly after dark, so agree a meeting point and keep small children in a carrier or by the hand. A bench at one of the food stalls makes a good base to watch from.
The animals are the part to think about. The snakes are a spectacle, and the Barbary macaques are wild animals kept on chains, which many families choose not to support. Their handlers expect payment for any photo. Watching from a distance avoids all of it.
Our evening food tour ends in the square with a guide who knows it well, which is an easy way to see it with children for the first time.