What your boys seem to be having is hidden or buried penis which is quite common in obesity due to the suprapubic fat covering the penis. If the boys are nor having any problem urinating, then there is nothing much to worry about. Losing weight or fat reduction by surgical approach in later life can help. Give a healthy, nutritious diet and ask your boys to exercise regularly. If the symptoms persist then a urologist should be consulted.
I sincerely hope that helps. Take care.