Of course, there are different levels of involvement that each dad wants to have with his kids.
Some are very hands off and leave most, if not all, parenting tasks up to their child's mother. Others are truly equals at home, sharing parenting tasks and being strongly involved in their child's life. And many dads are somewhere in the middle, being somewhat involved and taking on some parenting tasks, but falling short of being a true equal.
For those dads who are very involved in their child's life, it can be upsetting when the child has a strong preference for the other parent. Maybe the child cries when mom leaves the room, always goes to mom for comfort when he falls or cries, and as he gets older, always goes to mom for praise when he does well.
It can be even more upsetting if the child bypasses dad or pushes dad away while trying to get to mom when he is upset. Picture a toddler who has just fallen, is crying, and rejects dad's attempts to comfort him as he reaches for his mother. In such a situation, it is hard for dads to not take it personally and feel rejected.
But they shouldn't take it personally. It is quite normal for children to have a preference for one parent, usually the one that they spend more time with, and for that preference to sometimes change from one parent to the other. That should also be reassuring to moms who are in a similar situation, where their child has a preference for dad.
Even if it is normal behavior, that doesn't mean that you can't take steps to help avoid these types of situations.
The most important things to consider is that a strong preference for one parent likely means that the other parent needs to spend more time with their child and get more involved in day to day parenting activities, such as feedings, baths, bedtime routines, etc. Simply playing with your child from time to time is likely not going to be enough to build a strong relationship. And if you start in early infancy, you may even be able to avoid these types of problems.
When it isn't possible for the parent who isn't preferred to spend more time with their child, whether they travel a lot, are away, or simply work very long or odd hours, the other parent should take steps to keep them involved. This may mean frequent phone calls or simply talking about the other parent a lot, even when they aren't home.
It can also help if the preferred parent doesn't always try to rescue their child, especially when the other parent is already involved. That doesn't mean that you have to ignore or walk away from your child if he wants you, but you also don't always have to rush over to offer comfort if the other parent is already there.
If your child has already developed a very strong preference for one parent, in addition to the other parent spending more time alone with the child, it may help if all three of you do things together. As things go well, the preferred parent can then slowly withdraw from these activities.
Keep in mind that a preference can also develop when one parent doesn't spend that much time with their child, but when they do, they only do fun stuff. So maybe the other parent is busy with work outside the home, household chores, or is the disciplinarian in the family, and so the 'fun' parent is preferred. Sharing all duties, including playtime and discipline, can help to avoid this situation.
Whether the preference is for mom, dad, or even another caregiver, remember that even if you aren't the preferred parent, that doesn't mean that your child doesn't love and need you. Instead of feeling rejected or jealous, try to spend more time with your child, respect your child's bond with his other parent, and understand that these preferences are often temporary, may switch back and forth between parents over time, or may even change to the other parent later on.