Hey Mama! First of all, the American Academy of Pediatrics recommends that baby has nothing but breastmilk or formula for the first six months. This means no juice, water, cereal, or anything else.
At 4.5 months, your baby is not physically capable of eating solid foods. The gassiness is coming from his inability to digest the cereal properly and it's high concentration of iron. Commercial baby cereals have no nutritional value -- they are like eating paste!
The best way to do it is to watch your baby for signs of readiness for solid foods:
- The baby can sit up by himself without assistance
- The baby has teeth
- The baby shows interest in solid foods, grabbing yours or imitating your eating
- the baby has lost the tongue thrust reflex, which causes them to spit out anythign but a nipple that is put in their mouth.
Good first foods to start with are: mashed ripe banana, mashed ripe avocado. Just take a baby spoon and scrape a little of the fruit off and let him taste. The American Academy of Pediatrics also says that breastmilk (or formula) should be the MAIN source of nutrition for the baby's entire first year. Solid foods are tastes and introductions and supplements for the first year, not the main event!
On a side note, if you let the umbilical cord pulse until it is done at the moment of birth, your baby is not at risk of anemia in the first year and does not need supplemental iron in cereals.