Out of curiosity, if you have kids and want them to be friends and play together how closely would you have them?
Sil currently has a 4 year old and is trying for a second because she wants to give Z a playmate. She and Scott are only 6 months apart (adopted) and both loved having a sibling so close in age. Sil thinks 4 years apart would be perfect playmate age.
The people I know who had a sibling 4+ years difference generally hated each other until they were in their 20's, and definitely did not play or enjoy time with them when they were younger.
And omg..poor lady on tv got pregnant when her first baby was 9 months old. that's a lot of diapers.