The Census info suggests Gerrit lived with Anna & Isaac until he was about 7 or 8yrs old [when he spends 2 years visiting with his father's family?] then returns to Anna & Isaac at about 9yrs old."
I cannot find any of proof this in the census info. Could you provide the exact reference where this is to be found?
Knowing the children Anna or Isaac have baptised up to this date, it's reasonable to assume that Gerrit is one of the boys living with them in 1724 (when he would have been 7 or 8), then not in 1725-6, and then again in 1727.
We have no evidence for another child - so no reason to manufacture another scenario, when this one is perfectly tenable.
You appear invested in it not being so - but so far haven't provided a better explanation.