RootsChat.Com

I don't think this is a p.m. photo.
The pose doesn't look right.
Usually children are posed lying down either in a crib or mother's arms.
You do see some where children are posed to appear alive but I don't think this is one.
There was a practice I believe of some photographers giving problematic children
a drop of Laudanum to quiet them down but I don't know how common that was.
Skirts usually didn't come with pockets so where does one put one's hanky?

I have also been told that it could possibly be the uniform of the Machine Gun Corp

I'm afraid you were misinformed.
The uniform of the MGC was identical to the infantry uniform.

I don't want to be picky but it was 1916 when the economy
tunic was introduced.
The man is wearing riding breeches & a bandolier so does narrow it a bit.
Could be a driver RFA or possibly RE.
The uniform changed back to the pre economy version post war & then to the
WW2 style in the late 30's so could 1920'or 30's.

Good find AllanUk unfortunately I'm not seeing an MIC for him.

Not seeing a Thomas Liddle with the number you gave but there is
one with number 29644 in the Royal West Kents.
Really need his number.
There is a record for a Thomas William Liddle b.1887
no.  288244
Not him, wrong occupation.