I honestly think that the differences between having 1, 2, 3, 4 or 12 kids are small compared to the differences between individual women and families. A family of 2 children can be neglected, and a family of 7 children can each receive ample love and attention from their parents and carers. An only child can be outgoing, and one of 5 can be introverted. Two children 5 years apart can get along fine, while siblings one year apart can fight constantly or practically ignore one another.

With three kids, I wouldn't worry about one being left out. If two do something together, the other one has an opportunity for some time alone, with a parent, or with a friend (once they're a bit older). Or they may love to do everything as a group of three. Or they may all have very different interests and not do much together at all. Ultimately, you know better than anyone else what the right family shape is for you. If you love and care for however many children come into your life, you'll find ways to overcome any practical difficulties.