if you are going by train, the wetherspoons just across the main road via an underpass opposite the main central mk rail station is child friendly but WILL be heaving. All the pubs around Bletchley will be rammed. If you are driving you might want to stop in stony Stratford. 15mins to the ground from there.
wouldn't touch wetherspoons with kids.....Do not serve you with kids unless you are buying a meal....this has happened to us away at Wolves, Walsall, shrewsbury and Port Vale so be warned!