Since the baby being healthy is a basic consideration, then responsible prenatal care is important, along with basic baby/child proofing of the baby's living area, and basically being a responsible parent to try to keep the baby safe and healthy.
An example of someone not respecting the baby's developmental stage is for someone to try to force a baby at the crawling stage to walk. Among other things, crawling allows the baby's upper body to develop properly, and there are plenty of movement activities and games that a crawling baby can participate in.
Many school systems allow children to enroll as early as when three years old. You want the child entering school or school-like program ready to be taken to the next level, and certainly not behind.
Parents should work closely with the school teachers to be sure the child is putting forth a committed effort to being a good student. Sure the kid is at a beginning maturity level, but there is an age appropriate curriculum for a reason. Play is definitely mixed in, especially for the younger ages, but except for recess time, the play is purposeful play. Your kid will not learn much from the purposeful play if he/she acts as if class time is recess time.
Kids learn and mature at different rates, and of course the quality of instruction is a factor, but a good Physical Education goal is for the child to be capable enough in the perceptual motor skills to be ready to be transitioned into sports between the ages of 4-6 years old.
At 5 years old, typically there are T-ball (baseball), Pee Wee Soccer, and Pee Wee Basketball leagues to join. If able, I suggest allowing the child a formal introduction into the sport and some practice in the activity prior to the first day of practice. This, obviously, gives the child an edge. Ideally, the parent should try to make it possible for the child to get some very good coaching in the fundamentals of the sports he/she are participating in. This may also mean enrolling in camps or even small group or individual sessions. Learning the fundamentals at an early age is extremely important!
When the child is attending school and playing a sport, he/she is a student /athlete. Ideally, all the work and attention to detail to put the child in a position to be successful in both endeavors has paid off. Providing support for a child that is already headed in the right direction is a lot easier than doing so for one that is behind and struggling. It is also easier to get the child to “buy in” and take a genuine interest in school and athletics when they are a source of fun and adventure for the child. Ideally, through sports, school, church, etc…, the child will also gain friends and continue to develop socially. Performance in elementary school, academically and athletically, can set the tone for what follows.