No.
That's the simple answer. The more complex answer is that SWA no longer preboards families with young children, because too many people were abusing that privilege.
The new boarding pattern is that disabled passengers still may preboard, then A's (including any families with young children who happen to be holding A's), THEN any nuclear families that do not have A's but DO have children *under* age 5, then B's, then C's.
What you should do: Check in exactly 24 hours out, get A's, and head straight to the back of the plane. You should have no trouble finding 8 seats fairly close together.
FYI, Under the old system (as it was designed, not as it was abused) any NUCLEAR family travelling with a child under age 5 were allowed to preboard. No grandparents, aunts, uncles, etc., unless they happened to be disabled and eligible to preboard on their own account. Lots of times the gate agents looked the other way when extended family took advantage and preboarded with only one baby present. People even did things like going up to someone struggling with carrying a child and baggage and offering to help if they could pretend to be an aunt. Or even just asking if they could pretend to be an aunt and not even offering to carry something in return for the favor.