If I had to plan my family over again, I would put six years between each child. That way, a parent could enjoy and give all their attention to one child until that child went off to school OR was independent enough to do some school work/home learning.
That would also give the parent time to save $ for school/college/car.
That is just my opinion though. One would have to consider their own age when the family is started. If one's first child is born when one is 30 years old, one may not want to wait so many years.
Clearly, this is an individual choice with many factors to consider.
"Vaccines are like a box of chocolates. You never know what you're gonna get - acute hemorrhagic edema of infancy, allergies, anaphylaxis, asthma, autoimmune disease, diabetes, eczema, petit/gran mal seizures, fibromyalgia, Henoch-Schonlein purpua, Dravet's Syndrome, Retts Syndrome, Sweet's Syndrome, Hughes Syndrome, encephalitis, speech delay, tics, neurological damage, coma, ADEM, ADHD, AFP, ASIA, CFS, CRPS, GBS, ITP, JPA, JRA, LGS, LKS, MS, OMS, ORS, PANDAS, PANS, PINTANDS, POF, POTS, RA, SIDS, SJS, SLE, SPD, SUDS, TPI, the disease one is being vaccinated against, or death."
Paraphrased from "Forrest Gump".
List from the drug companies' own package inserts that come with their product as required by law.