J.B.
C.,
Oatmeal is not recommended for a 5 month old. It is best to hold off on solids until the baby is at least 6 months old. If you are still breastfeeding, continue to do so and often to flush out the baby's system. If you are formula feeding, it is still better to wait and the first recommended cereal is a rice cereal. Rice is easier for the baby to digest.
The baby does not have the enzymes to digest cereals until at least 6 months and this is variable. Sometimes later than 6 months is better for some babies.
Signs of readiness for solids include:
Absence of tongue thrust.
Able to sit up with support.
Baby can grasp food and put it in his/her mouth.
The baby is clearly not satsified after breastfeeding.
Putting things into the mouth is not a sign of readiness. It is imitative behavior. If this is happening, give the baby "mouth toys" - certain toys to put in the mouth when the family is eating.
I hope this helps you.
J. Bouchet-Horwitz, NP, IBCLC