Dear Mr. Dad: We have two boys, ages four and nine. The nine-year-old has no problem sleeping in his own bed, but the four-year-old constantly wants to sleep with my husband and me. I don't mind an occasional "sleep over" - especially when my husband is away on business and the bed seems so empty. But lately, my son wants to be in our bed every night. That seems a little old to me. Is co-sleeping with a four-year-old okay?