T-shirt sizing help for a 3 1/2 year old's gift

[smomom]

I want to surprise my nephew (and SIL) with an "I'm the Big Brother" t-shirt, but I have no idea what size he wears. He is 3 1/2 years old - born on 10/2/2000. He may be a little tall for his age.

My sizing choices are 5/6T or 6/8 Small Youth. I don't want it to be too small. What size do you suggest that I order?

thanks so much!

[luvbeinmama]

I would go with the 5/6T. My DS is fitting nicely into 4T & 5T shirts right now. He is average ht/wt for his age.