I think relationships, all relationships, have highs and lows, ups and down and even being stuck in a rut.
Spark things up with him. Put the kids to bed early and set the table with your finest dishware and crystal, cook a great meal and have a date in your dining room. You two just need to reconnect and be yourselves, not a mommy or a daddy every once and a while. Be honest with him and let him know that you are feeling disconnected and want more sparks between you. If sex is, as you say, not interesting, then MAKE it interesting!! Men need to be told what a woman likes in bed. They often THINK they know what to do, but some guys need a little nudge.