First, let me say that I love Cym's reason for having more children--because in her heart it seems like the right thing to do. That same reason--it feels like the right thing--is probably also the best reason to have only one child. I think this applies whether children are gifted or not. The other reason to either have or not have children is because sometimes the decision is beyond our control and then we deal with our circumstances (whether reproductive problems or an unplanned pregnancy) as best we can.
All that aside, though, I am interested in any real data that is out there on gifted children doing better with siblings. We fought through a ton of stereotypes masquerading as real information from experts on only children when we were making our decision. We ended up reading Maybe One by Bill McKibben and You and Your Only Child, both of which clearly refuted any evidence that only children, in general, are harmed by being onlies.
Only child research is difficult because people often do have only children for reasons beyond their control and those other reasons can really confound the data. It's not because the child is an only that s/he has problems; it's because the parents are dealing with unresolved grief over their infertility or one parent has died or there is a divorce etc etc. Unless you control for these variables, comparisons between onlies and multiple sibling families are unfair.
I can certainly say that for us, having a gifted first child contributed to his being an only. I remember how intensely he needed my constant attention, conversation, eye contact and stimulation when he was an infant and toddler. I kept thinking that there was no way I could meet his needs if I had another child--heck I couldn't even remember to feed the cat!! LOL I don't like failure and I knew that trying to meet the needs of more than one child would be a recipe for failure. DS is now 12 and he is absolutely thriving--happy, confident, adventurous, and very popular. There are probably many reasons for that, but I cannot imagine that he could have been any happier if he'd had a sibling (even though he may not have been any less happy either...)
