What age should we be to stop our children from crossing us in prayer?
Actually, we need to try and not allow any children to pass between us and the sutrah as much as we can. However, if they still pass in front of us then there is nothing upon us as we took by the means (sutrah and trying to stop them). There is no specific age.
Yet, if the girl (only girls) reached puberty and passed between the person praying and his sutrah, the prayers become cut and invalid. The person praying has to cut and repeat it.