"Tengo dos hijos y les compro camisetas."
Translation:I have two sons and I buy them t-shirts.
Does anyone know why this is compro instead of comprar? I thought you only conjugate once, with tengo in this case.
It's a compound sentence, two sentence joined by a conjunction.
"Les compro camisetas."
This sentence can stand on its own, so it has (needs) a conjugated verb.
It's compro because it's translating into 'I buy'. You can have more than one conjugated verb in a sentence as long as the verbs are separated as DanD_8 rightly points out.
What you can't have is two conjugated verbs sitting next to each other because they won't make sense, it's then that you have to use the infinitive of the second verb. Consider:
Tengo compro - I have, I buy? Doesn't make sense. Instead you would use the infinitive verb form:
Tengo comprar - I have 'to buy'... now it makes sense.