My family splits meals frequently. We are a family of 5 and my 14 yo and 11 yo have been considered "adults" for a few years now. 4 adult sized entrees and desserts plus 1 child entree and dessert are more often than not too much food for us.
We often split and use 3 adult credits and 1 child credit or just 3 adult credits. I have never gotten a funny look or had any issue. The wait staff will sometimes pause about our drink orders because if we order 5 sodas, there is a charge for one or more of them. I don't care about the extra charge but I guess they want to make sure I know.
There are some restaurants that don't allow splitting. Via Napoli is one of them. We had split there once in the past but knew going in on the last two trips that we wouldn't be allowed to. There may be others as well. Obviously you can't split at buffets or any type of all you can eat place.