Your invitation is cute and the tickets are a darling idea!
The decorated paint tins would be a excellent idea and could customize the contents to 2-3 age levels. Playdoh was always a great thing for my kids when small (they are all in their 20's now). You could add small lego set for older boys and of course lipgloss & nail polish for gals.
My first thought tho to keep with the invitation theme was the old fashion wooden train whistles! I saw some recently at the Dollar Tree. Don't know if you have that chain where you are. Are you from Lancaster PA or OH? Those are the only 2 Lancasters I am familiar with.
Have a great time with party and take oddles of pictures cause they grow up quickly.
Please post more pics when you complete the favors.