In your practice, how are children handling the first MMR at 4-5 years old? In this age range, have you seen any regression/behavioral/gastro changes following this vaccine that you are concerned about? Do those in the 6-10 age range handle the vaccine even better?
Also, have you ever associated the 5th DTaP with causing hypersensitivity and resulting food allergies, or is this dose relatively well tolerated?
When my son was 3.5, he had large, round constipation followed by encopresis for months following the varicella vaccine. He just turned five, and I am not sure when to proceed with the MMR and the second varicella vaccine. Unfortunately, he does not have a positive titer from the first varicella vaccine.
They are handling it well at 4 or 5. I don't really have any data or observed experience comparing this to any 8 or 10 year olds.
5th DTaP is usually well tolerated. I have seen an occasional reaction, but pretty rare.
With that history of varicella reaction, I would advise against getting another dose of that, unless there's a special reason you need it.
I know it isn't easy to make these decisions. Vaccine reactions are fairly unpredictable, and I know it isn't easy to feel comfortable with these. There's always going to be a small chance of a tough reaction.