My opinion (only since you asked)...I think they are too young to decide for themselves. I'm married and in my experience watching my kids grow up I can see them sometimes leaning more toward one parent for a while and then swaying back to the other. Also depending on the activities that they are doing they prefer doing some things with their father and other things with me. When they were really young my eldest son had a preference to me while my youngest had a preference to his father. I happened to have been in an accident when my youngest son was 3mths old, so I couldn't do as much with my youngest son. My H had to take care of him a lot more than he had to take care of my eldest son. Perhaps that is were the bond developed? Today they are more comfortable with me in certain things and my H in other things. There is no favourite parent, although they do prefer going to the shop with their father because they are more inclined to get what they want
. I think children ideally need interaction with both parents. The word "no" is also something that they NEED to hear. There are boundaries and they need to conform to those boundaries. Unless you are trying to protect them from something happening at your ex's house I don't think they should be given the option. They should be taught to treat both parents with equal respect, and be careful to not allow them to manipulate you. I think for me it is kind of like disciplining children. We don't like doing it, but if we don't, we end up raising brats. You could look at the situation of making them eat fruit and vegetables - they may not like it, but that is what they need.
I think you know what what your children need. The easy option is not always the right option.
B2W