Others will have opinions on this one too...
For me -
Rhode Island Reds (boys) are super gentle and sweet. The two that I have do not fit the stereo type of being aggressive. (I adopted these guys.)
Buff Opingtons (girl) - my is super sweet and friendly. The boys are more skittish, but generally docile. I've raised these guys from babies. Correction - the two boys I raised as chicks are gentle. The ones I adopted, not so gentle, but they are mellowing out now.
White Leghorns (girls) - I have one that is sweet and adventurous. She has no problem coming up and talking to me.
Austrolorps (girls) - skittish.
Rocky Barre (boys) - forget it. These two are the noisest of the whole gang.
Carolina Sex Link (boy) - the LOUDEST dang chicken I have.
Americuanas (boys) - not bad. Mine are lap roosters, but they didn't start off that way.
*** things to consider when introducing your grandson to the chickens --
- how loud are the birds?
- how docile are they?
- do they have names your grandson can pronounce?
- do they have distinct features to make it easy for your grandson to identify them?
Please don't have your grandson meet birds with the intention of feeding them. The sudden interest in the food might scare your grandson.

Let him watch and observe the birds. Sit near the birds and read the birds & your grandson a story. The birds might come over and listen. (Mine do.)