echo songs are good for counter-acting distraction and/or frustration. I usually start with echo songs to sort of get an idea of what the group is like.

Found a Peanut
My hat it has three corners
Head, Shoulders, Knees and Toes
Dora had a camel (which I think may be properly called 'Doris the camel?)
Father Abraham
Farmer in the Dell
Mairzy doats

If the kids have a great time with you (no doubt they will) they'll be singing bits and phrases of the songs at home. You might want to save the tacky/gross ones for late in the program..after the parents have had a chance to form a high opinion of you.

It sounds like a fun project!