Of course it's okay! Colostrum is liquid gold and full milk is the best possible long term growing and brain food for babies... A mix of the two is an awesome thing.
So is it okay for them to drink transitional milk?
Transitional starts a couple days after baby is born
It comes after the baby is born, while pregnant it's colostrum or some call it pre milk. Actual milk will come in about 10-14 days after baby. There's 3 stages of milk, 1st colostrum 2nd is transitional milk and last is mature milk.
First its colostrum then the milk :)